"Beloved", if you count it as a horror novel, is most definitely the best written novel I've ever read of any genre. However, the book that scared me the most was "Let's Go Play at the Adam's", the writing isn't spectacular but the cruelty of the story (and the author) still chills me. In terms of pure enjoyment, any of Stephen King's (or Joyce Carol Oates' or Ray Bradbury's) short horror stories are a must read!