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.
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: