There is no question that there is a glut of books covering introductory material for Wiccans and Witches.  What books cover intermediate to advanced topics?  One way to get into intermediate to advanced study is to work from books such as Deborah Lipp's excellent "The Study of Witchcraft " (San Francisco: Weiser Books, 2007.)  Another way is to pick your favourite introductory text and look at its recommended reading list or bibliography.  Here's my own categorized list to help out seekers looking for something beyond the introductory.

General Reference

These books are important because they help build context.  Use them to look up specific topics and historical people to get a better idea of how they fit into the whole.

Buckland, Raymond "The Witch Book: The Encyclopedia of Witchcraft, Wicca, and Neo-Paganism," (Detroit MI: Visible Ink Press, 2002.)

Drury, Nevill "The Dictionary of the Esoteric," (London UK: Watkins, 2002.)

Greer, John Michael "The New Encyclopedia of the Occult," (St. Paul MN: Llewellyn, 2003.)

Guiley, Rosemary Ellen "Harper's Encyclopedia of Mystical & Paranormal Experience," (New York NY: Harper's, 1991.)

Guiley, Rosemary Ellen "The Encyclopedia of Witches & Witchcraft, Second Edition," (New York NY: CheckMark Books, 1999.)

Jordan, Michael "Witches: An Encyclopedia of Paganism and Magic," (London UK: Kyle Cathie Ltd., 1996.)

Rabinovitch, Shelley & Lewis, James (eds.) "The Encyclopedia of Modern Witchcraft and Neo-Paganism," (New York NY: Citadel Press, 2002.)

Riland, George "The New Steinerbooks Dictionary of the Paranormal," (New York NY: Warner Books, 1980.)

Mystery Religions

Since Wicca is often identified as a modern mystery religion it makes sense to study historical mystery religions to learn about where Wicca draws its inspiration.  

Angus, S. "The Mystery-Religions," (New York NY: Dover, 1975.)

Burkert, Walter "Greek Religion," (Cambridge MA: Harvard University Press, 2000.)

Daraul, Arkon "Secret Societies: A History," (New York NY: MJF Books, 1989.)

David-Neel, Alexandra "Magic and Mystery in Tibet," (New York NY: Dover, 1971.)

Farrar, Janet & Bone, Gavin "Progressive Witchcraft: Spirituality, Mysteries & Training in Modern Wicca," (Franklin Lakes NJ: New Page Books, 2004.)

Grimassi, Raven "The Wiccan Mysteries: Ancient Origins & Teachings," (St. Paul MN: Llewellyn, 1997.)

Harrison, Jane Ellen "Prolegomena To the Study of Greek Religion," (Princeton NJ: Princeton University Press, 1991 edition but originally published in 1903.)

Meyer, Marvin W. (ed.) "The Ancient Mysteries: A Sourcebook of Sacred Texts," (Philadelphia PA: University of Pennsylvania Press, 1999.)

Mysticism

Wicca and many modern witchcraft paths also draw on mysticism.  The following books explore this topic in general and also in relation to occultism.

Harvey, Andrew "The Direct Path: Creating a Journey to the Divine Using the World's Mystical Traditions," (New York NY: Broadway Books, 2000.)

Hedsel, Mark "The Zelator: A Modern Initiate Explores the Ancient Mysteries," (London UK: Century Books Ltd., 1998.)

Horgan, John "Rational Mysticism: Spirituality Meets Science in the Search for Enlightenment," (New York NY: Mariner Books, 2003.)

James, William "The Varieties of Religious Experience," (New York NY: Touchstone, 1997.)

Johnson, Robert A. "Ecstasy," (San Francisco CA: HarperSanFrancisco, 1987.)

LeShan, Lawrence "The Medium, the Mystic, and the Physicist," (New York NY: Viking Press, 1974.)

Nema, "The Way of Mystery: Magick, Mysticism & Self-Transcendence," (St. Paul MN: Llewellyn, 2003.)

Sinetar, Marsha "Ordinary People As Monks And Mystics," (New York NY: Paulist Press, 1986.)

Teasdale, Wayne "The Mystic Heart," (Novato CA: New World Library, 2001.)

Underhill, Evelyn "Practical Mysticism," (Columbus OH: Ariel Press, 1942.)

Underhill, Evelyn "Mysticism," (Oxford UK: Oneworld Publications, 2001.)

Wiccan Foundations

While the following are clearly introductory texts they are valuable as solid presentations of Wiccan foundations.  They give the "what" of Wicca, and in some cases also provide introductory explanations of the "why."

Buckland, Raymond "Buckland's Complete Book of Witchcraft," (St. Paul MN: Llewellyn, 1986.)

Buckland, Raymond "The Tree: The Complete Book of Saxon Witchcraft," (New York NY: Weiser, 1974.)

Cunningham, Scott "Wicca: A Guide for the Solitary Practitioner," (St. Paul MN: Llewellyn, 1990.)

Curott, Phyllis "Witch Crafting," (New York NY: Broadway Books, 2001.)

Farrar, Janet & Farrar, Stewart "A Witches Bible," (Blaine WA: Phoenix Publishing, 1996.)

Grimassi, Raven "Spirit of the Witch," (St. Paul MN: Llewellyn, 2003.)

Shanddaramon, "Self-Initiation for the Solitary Witch," (Franklin Lakes NJ: New Page Books, 2004.)

Starhawk "The Spiral Dance," (San Francisco CA: Harper & Row, 1979.)

Valiente, Doreen "Witchcraft for Tomorrow," (Blaine WA: Phoenix Publishing, 1978.)

Intermediate To Advanced Wicca

This list is a partial selection of excellent texts for the intermediate to advanced Wiccan or Witch.  Be sure to check the bibliographies and recommended reading lists in these books to get suggestions for further research.

Berg, Wendy & Harris, Mike "Polarity Magic," (St. Paul MN: Llewellyn, 2003.)

Cat, Grey "Deepening Witchcraft," (Toronto Canada: ECW Press, 2002.)

Fisher, Amber Laine "Philosophy of Wicca," (Toronto Canada: ECW Press, 2002.)

Grimassi, Raven "Crafting Wiccan Traditions," (St. Paul MN: Llewellyn, 2008.)

Gruagach, Ben "The Wiccan Mystic," (Eden Prairie MN: WitchGrotto Press, 2007.)

Harrow, Judy "Spiritual Mentoring," (Toronto Canada: ECW Press, 2002.)

Lipp, Deborah "The Elements of Ritual," (St. Paul MN: Llewellyn, 2003.)

Rauls, Venecia "The Second Circle: Tools for the Advancing Pagan," (New York NY: Citadel Press, 2004.)

Reed, Ellen Cannon "The Heart of Wicca," (York Beach ME: Weiser, 2000.)

Sylvan, Dianne "The Circle Within," (St. Paul MN: Llewellyn, 2003.)

Telesco, Patricia "Advanced Wicca," (New York NY: Citadel Press, 2000.)

Magick

The following texts are considered to be introductory but are much more focused and sophisticated in their presentation of the material than many other beginner books.  Most of these are probably too difficult for most beginners unless they have read a few other simpler introductory magick texts first.  (The only exception is "Grimoire for the Apprentice Wizard" by Oberon Zell-Ravenheart – it is perfect as a first book on the magickal path.)

Bardon, Franz "Initiation Into Hermetics," (Wuppertal Germany: Ruggeberg-Verlag, 1993.)

Bardon, Franz "The Practice of Magickal Evocation," (Wuppertal Germany: Ruggeberg-Verlag, 1991.)

Bonewits, Isaac "Real Magic," (York Beach ME: Weiser, 1990.)

Chumbley, Andrew "Azoetia," (Chelmsford UK: Xoanon Publishing, 2002.)

Crowley, Aleister "Magick In Theory and Practice," (New York NY: Dover, 1976.)

Duquette, Lon Milo "The Magick of Thelema," (Boston MA: Weiser, 1993.)

Fortune, Dion "Sane Occultism & Practical Occultism In Daily Life," (Bath UK: Aquarian Press, 1987.)

Fortune, Dion "Esoteric Orders and Their Work," (York Beach ME: Weiser, 2000.)

Fortune, Dion "The Training & Work of an Initiate," (York Beach ME: Weiser, 2000.)

Fortune, Dion "Aspects of Occultism," (York Beach ME: Weiser, 2000.)

Fortune, Dion & Knight, Gareth "An Introduction to Ritual Magic," (Loughborough UK: Thoth Publications, 1997.)

King, Francis & Skinner, Stephen "Techniques of High Magic," (New York NY: Warner Destiny Books, 1976.)

Kraig, Donald Michael "Modern Magick," (St. Paul MN: Llewellyn, 1988.)

Lupa "Fang and Fur, Blood and Bone: A Primal Guide to Animal Magic," (Stafford England: Immanion Press, 2006.)

Murphy-Hiscock, Arin "Power Spellcraft for Life," (Avon MA: Provenance Press, 2005.)

Nema, "Maat Magick," (York Beach ME: Weiser, 1995.)

Newcomb, Jason Augustus "The Book of Magick Power," (Sarasota FL: The New Hermetics Press, 2007.)

Regardie, Israel "Foundations of Practical Magic," (Guildford UK: Aquarian Press, 1982.)

Watson, Nancy B. "Practical Solitary Magic," (York Beach ME: Weiser, 1996.)

Zell-Ravenheart, Oberon "Grimoire for the Apprentice Wizard," (Franklin Lakes NJ: New Page Books, 2004.)

Wiccan, Pagan, And Magickal History

Most books on Wicca, Witchcraft, and occultism give a chapter or two on history – the following resources expand the topic in much greater depth.  

Betz, Hans Dieter (ed.) "The Greek Magickal Papyri in Translation: Second Edition," (Chicago IL: University of Chicago Press, 1996.)

Bonewits, Isaac "Witchcraft: A Concise Guide," (USA: Earth Religions Press, 2001.)

Bonewits, Isaac "Bonewits's Essential Guide to Witchcraft and Wicca," (New York NY: Citadel Press, 2006.)

Coughlin, John J. "The Wiccan Rede: A Historical Journey," on the web at http://www.waningmoon.com/ethics/rede.shtml

Council of American Witches "The Principles of Wiccan Belief," on the web at http://www.religioustolerance.org/wic_stat1.htm

Crowther, Patricia "High Priestess: The Life & Times of Patricia Crowther," (Blaine WA: Phoenix Publishing, 1998.)

Davies, Morganna & Lynch, Aradia "Keepers of the Flame: Interviews with Elders of Traditional Witchcraft in America," (Providence RI: Olympian Press, 2001.)

Davis, Morgan – GeraldGardner.com website, found on the internet at http://www.geraldgardner.com

Gardner, Gerald "Witchcraft Today," (New York NY: Citadel Press, 2004.)

Gardner, Gerald "The Meaning of Witchcraft," (New York NY: Citadel Press, 2004.)

Graf, Fritz "Magic in the Ancient World," (Cambridge MA: Harvard University Press, 2002.)

Griffyn, Sally "Wiccan Wisdomkeepers," (York Beach ME: Weiser, 2002.)

Heselton, Philip "Gerald Gardner and the Cauldron of Inspiration," (Milverton UK: Capall Bann Publishing, 2003.)

Heselton, Philip "Wiccan Roots: Gerald Gardner and the Modern Witchcraft Revival," (Milverton UK: Capall Bann Publishing, 2000.)

Hutton, Ronald "The Triumph of the Moon," (Oxford UK: Oxford University Press, 1999.)

Hutton, Ronald "Witches, Druids and King Arthur," (Oxford UK: Oxford University Press, 2003.)

Jones, Prudence & Pennick, Nigel "A History of Pagan Europe," (New York NY: Barnes & Noble, 1995.)

Kelly, Aidan A. "Inventing Witchcraft," (Loughborough UK: Thoth Publications, 2007.)

Leitch, Aaron "Secrets of the Magickal Grimoires: The Classic Texts of Magick Deciphered," (St. Paul MN: Llewellyn, 2005.)

Lewis, James R. (ed.) "Magickal Religion and Modern Witchcraft," (Albany NY: State University of New York Press, 1996.)

Mathiesen, Robert and Theitic "The Rede of the Wiccae: Adriana Porter, Gwen Thompson and the Birth of a Tradition of Witchcraft," (Providence RI: Olympian Press, 2005.)

Thomas, Shea "Origins of the Rede Poem," on the web originally at http://www.draknetfree.com/sheathomas/poem.html but also available in a partial archive at http://web.archive.org/web/20031218001055/www.draknetfree.com/sheathomas/index.html

Vale, V. & Sulak, J. "Modern Pagans: An Investigation of Contemporary Paganism," (San Francisco CA: RE/Search Publications, 2001.)

Valiente, Doreen "The Rebirth of Witchcraft," (Custer WA: Phoenix Publishing, 1989.) 

Wilby, Emma "Cunning Folk and Familiar Spirits," (Brighton UK: Sussex Academic Press, 2005.) 

Wilson, Colin "The Occult," (New York NY: Vintage Books, 1973.)

Wilson, Colin "Mysteries," (Toronto Canada: Granada, 1983.)

Wilson, Colin "Beyond the Occult," (London UK: Corgi Books, 1989.)

Witt, R. E. "Isis in the Ancient World," (Baltimore MD: Johns Hopkins University Press, 1971.)

Trance And Altered States Of Consciousness

Mystical and mystery religions tend to employ altered states of consciousness, or ecstatic states, as one of their primary techniques.  The following books provide more on this topic.

Amoda "Moving Into Ecstasy," (London UK: Thorsons, 2001.)

Ash, Mel "Shaving the Inside of Your Skull: Crazy Wisdom for Discovering Who You Really Are," (New York NY: G. P. Putnam's Sons, 1996.)

Crabtree, Adam "Trance Zero," (Toronto Canada: Somerville House Publishing, 1997.)

Endredy, James "Earthwalks for Body and Spirit," (Rochester VT: Bear & Co., 2002.)

Heller, Steven & Steele, Terry "Monsters and Magickal Sticks: There's No Such Thing As Hypnosis," (Tempe AZ: New Falcon Publications, 1987.)

Huxley, Aldous "The Doors of Perception," (New York NY: Harper & Row, 1954.)

Hyatt, Christopher S. "Undoing Yourself with Energized Meditation and Other Devices," (Tempe AZ: New Falcon Publications, 2002.)

Lawrence, D.J. (ed.) "The Best of Konton Magazine," (Tokyo: Konton Publishing, 2005. http://www.chaosmagic.com )

Mishlove, Jeffrey "The Roots of Consciousness," (New York NY: Marlowe & Co., 1993.)

Guided Meditation And Pathworking

Guided meditations were a standard part of Golden Dawn practices and made their way into other magickal groups including Wicca.  The following focus on how to do these types of magickal explorations, many with scripts to follow for the journey.

Ashcroft-Nowicki, Dolores "The Initiate's Book of Pathworkings," (York Beach ME: Weiser, 1999.)

Galenorn, Yasmine "Magickal Meditations," (Toronto Canada: The Crossing Press, 2003.)

Houston, Jean & Masters, Robert "Mind Games: The Guide to Inner Space," (Wheaton IL: Theosophical Publishing, 1998.)

Houston, Jean "The Search for the Beloved," (Los Angeles CA: Jeremy P. Tarcher, 1987.)

Houston, Jean "The Hero and the Goddess," (New York NY: Ballantine Books, 1992.)

Kaplan-Williams, Strephon "The Jungian-Senoi Dreamwork Manual," (Novato CA: Journey Press, 1988.)

LeShan, Lawrence "How To Meditate," (New York NY: Bantam, 1975.)

Mariechild, Diane "The Inner Dance," (Freedom CA: The Crossing Press, 1987.)

Stewart, R. J. "Advanced Magickal Arts," (Shaftesbury UK: Element Books, 1988.)

Stewart, R. J. "Earth Light," (Shaftesbury UK: Element Books, 1992.)

Stewart, R. J. "Power Within The Land," (Shaftesbury UK: Element Books, 1992.)

Stewart, R. J. "The Living World of Faery," (Lake Toxaway NC: Mercury Publishing, 1999.)

Stewart, R. J. "The Underworld Initiation," (Guildford UK: Aquarian Press, 1985.)

Warren-Clarke, Ly & Matthews, Kathryn "The Way of Merlyn: The Male Path in Wicca," (Dorset UK: Prism Press, 1990.)

Wilson, Paul "The Calm Technique," (New York NY: Barnes & Noble, 1999.)

Devotions And Worship

Wicca is first and foremost a religion.  These books provide insight into how one can emphasize devotions and worship in Pagan practice.

Crowfoot, Greg "Crossroads: The Path of Hecate," (San Diego CA: Aventine Press, 2005.)

D'Este, Sorita "Hekate: Keys to the Crossroads," (London England: Avalonia, 2006.)

De Grandis, Francesca "Goddess Initiation," (San Francisco CA: HarperSanFrancisco, 2001.)

Freeman, Mara "Kindling the Celtic Spirit," (San Francisco CA: HarperSanFrancisco, 2001.)

Gillotte, Galen "Book of Hours: Prayers to the Goddess," (St. Paul MN: Llewellyn, 2001.)

Gillotte, Galen "Book of Hours: Prayers to the God," (St. Paul MN: Llewellyn, 2002.)

Harrow, Judy (ed.) "Devoted To You: Honoring Deity in Wiccan Practice," (New York NY: Citadel Press, 2003.)

Houston, Jean "The Passion of Isis and Osiris," (New York NY: Ballantine/ Wellspring, 1995.)

Kondratiev, Alexei "The Apple Branch: A Path to Celtic Ritual," (New York NY: Citadel Press, 2003.)

Laurie, Erynn Rowan "A Circle of Stones: Journeys & Meditations for Modern Celts," (Chicago IL: Eschaton Productions Inc., 1995.)

Masters, Robert "The Goddess Sekhmet: Psycho-spiritual Exercises of the Fifth Way," (St. Paul MN: Llewellyn, 1991.)

Matthews, Caitlin & Matthews, John "The Western Way," (London UK: Arkana/ Penguin, 1994.)

Newcomb, Jason Augustus "21st Century Mage: Bring the Divine Down to Earth," (York Beach ME: Weiser, 2002.)

Reed, Ellen Cannon "Circle of Isis: Ancient Egyptian Magic for Modern Witches," (Franklin Lakes NJ: New Page Books, 2002.)

Rhea, Lady Maeve "Summoning Forth Wiccan Gods and Goddesses," (New York NY: Citadel Press, 1999.)

Starhawk "The Twelve Wild Swans," (San Francisco CA: HarperSanFrancisco, 2001.)

Group Work And Community

Many Wiccans get involved in starting up or running their own spiritual community groups or covens.  These resources provide a wealth of practical tips for building community.

Bonewits, Isaac "Advanced Bonewits Cult Danger Evaluation Frame," found on his website at http://www.neopagan.net/ABCDEF.html.

Bonewits, Isaac "Rites of Worship: A Neopagan Approach," (USA: Earth Religions Press, 2003.)

Campanelli, Pauline & Campanelli, Dan "Circles, Groves & Sanctuaries: Sacred Spaces of Today's Pagans," (St. Paul MN: Llewellyn, 1992.)

Harrow, Judy "Wicca Covens," (Secaucus NJ: Citadel Press, 1999.)

Haugk, Kenneth C. "Antagonists in the Church: How to Identify and Deal with Destructive Conflict," (Minneapolis MN: Augsburg Publishing, 1988.)

Horowitz, Claudia "The Spiritual Activist," (New York NY: Penguin Putnam, 2002.)

K, Amber "Covencraft: Witchcraft for Three or More," (St. Paul MN: Llewellyn, 1998.)

K, Amber "Ritual Craft," (St. Paul MN: Llewellyn, 2006.)

McCoy, Edain "Inside a Witches' Coven," (St. Paul MN: Llewellyn, 1997.)

Peck, M. Scott "The Different Drum: Community Making and Peace," (New York NY: Touchstone/ Simon & Schuster, 1987.)

Pike, Sarah M. "Earthly Bodies, Magickal Selves: Contemporary Pagans and the Search for Community," (Los Angeles CA: University of California Press, 2001.)

Plant, Judith (ed.) "Healing the Wounds," (Toronto Canada: Between the Lines, 1989.)

Shaffer, Carolyn R. & Anundsen, Kristin "Creating Community Anywhere," (New York NY: Tarcher/Putnam, 1993.)

Starhawk "Dreaming the Dark," (Boston MA: Beacon Press, 1988.)

Starhawk "Truth or Dare," (San Francisco CA: Harper & Row, 1990.)

Walker, Wren & Jung, Fritz — the Witchvox website, found on the internet at http://www.witchvox.com, is the best Pagan networking resource bar none.