Bane, Theresa. Encyclopedia of Vampire Mythology. McFarland, 2010.Bunson, Matthew. The Vampire Encyclopedia. Random House International, 2001.Curran, Bob. Encyclopedia of the Undead: a Field Guide to Creatures That Cannot Rest in Peace. New Page Books, 2006.Guiley, Rosemary. The Encyclopedia of Vampires, Werewolves, and Other Monsters. Checkmark Books, 2005.Hallab, Mary Y. Vampire God: the Allure of the Undead in Western Culture. SUNY Press, 2009.Melton, J. Gordon. The Vampire Book: The Encyclopedia of the Undead. Visible Ink Press, 2010.Regan, Sally. The Vampire Book. DK Pub., 2009.
Most of these should be available as ebooks on Amazon, Apple, or Google. Isn't technology great?
What I find interesting about these books is that they include references to vampire-like creatures from across world mythology, including creatures you might not ordinarily associate with vampires like the Chinese húlijīng or "fox fairy".