I can't recommend Bram Stoker's Dracula enough to those who've never read or haven't read it in a long time.
I'm going to be teaching it to my English classes in a few weeks, to coincide with Halloween.
Also, there's a sequel of sorts to Dracula called The Historian by Elizabeth Kostova which I've heard is quite good. I'm going to be re-reading Dracula this weekend to prepare for teaching it.
Before I re-read Dracula, I'll be reading Raymond Florescu's fascinating In Search of Dracula, which I also highly recommend as good Halloween non-fiction.
So it's going to be In Search of Dracula, Dracula, and The Historian for me.
I also recommend the works of Poe and Lovecraft. You just can't go wrong with the classics during this time of year.