I don't really know if there is any book I've read more than five times. I don't actually keep count. But I would have to say the ones I've re-read the most often over the years are either The Earthsea Trilogy by Ursula K. LeGuin or A Wrinkle in Time by Madeliene L'Engle. All of those are quite well worn on my shelves, and I still get the urge to read them now and again.
I guess I like the dark overtones to the Earthsea books, and the way LeGuin packs so much detail and emotion into what are really rather small books.
And the L'Engle is just one of those books that feels good to read. I found it very early in my fantasy reading years, and it always just gives me pleasure, even though I know the story inside out by now. Again, the author manages to put a lot of story in a relatively small package.