SF and fantasy tickle the imagination in ways that no other genre can, I love thinking outside of the real world and looking beyond the everyday. Terry Goodkind was a favorite, as well as the Wheel of Time books by Robert Jordan (although seriously it's time to wrap it up). The Game of Thrones books are the newest big thing, but really I'd rather watch the TV show and save myself some time for other things.
I suppose I should give a shout out to good old animal stories. I read books about animals voraciously when I was a kid, and as I grew older it tapered down to almost never. Watership Down by Richard Adams is still one of the best books I've ever read. I must have read it a dozen times when I was a teenager and it never gets old. There are stories within stories, trials and perseverance, but without the heartbreak of most animal books. Black Beauty and Whitefang as well as others were hard to read at times because of the horrible cruelty inflicted upon the characters. I don't think I could ever write a book that didn't have animals as a major force within the story.
What are your favorites? If you wanted everyone to read just one book what would it be?