Dracula by Bram Stoker.
The version I like to read the best is an annotated edition, with notes by Leonard Wolf.
I've recently learned of a great resource for book lovers, BookDrum.com, which has an entry for Dracula. If you follow the link, you'll find all sorts of background material, maps, links, etc.
My favorite movie versions include of course, Dracula, the 1931 version starring Bela Lugosi; Bram Stoker's Dracula with Gary Oldman in the starring role and Dracula: Dead and Loving It, starring Mel Brooks and Leslie Nielson.
Check out the links! Enjoy!