The following websites are in no particular order, are not a representative sample of what is available, and are very different from each other. Enjoy the journey.
Drawing Down The Moon by Margot Adler
Classic witch texts, including Margaret Murry's The Witch Cult in Western Europe :
Biographies of famous witches, from folkloric sources through contemporary times:
By feminist scholar Max Dashu: Witches and Pagans
Hunting for Witches in the Family Tree is a commercial and commercialized site,
but with interesting information and links:
A research guide to the history of witchcraft, from the University of Pennsylvania:
Deborah Harkness teaches the history of science at the University of Southern California and has written a best-selling fiction trilogy with witches as many of the main characters.
Her website has lots of really interesting stuff:
Websites by law professor Douglas Linder of the University of Missouri, Kansas City:
Lynn Thorndike's A History of Magic and Experimental Science (8 volumes) is discussed in a slightly bizarre website: