The Overlook Film Encyclopedia: Horror
This is the best single volume book on the horror film, the definitive reference work devoted to the subject. It contains entries on every movie even remotely connected to the genre, whether it is a 19-century silent, a grade "Z" schlocker, or an "art" film by the likes of Fritz Lang orIngmar Bergman.  Each entry contains a full list of credits and a descriptive review. Hardy writes about horror movies with such enthusiasm and intelligence that you feel you're getting the low down on the genre from a sincere and learned friend.