The Lord of the Rings by J. R. R. Tolkien.

Don't think I need to explain what it's about at this point. As to what drew me to read it multiple times, that's due to it still being the greatest high fantasy story ever created. And it's a very balanced story. Every character, even the most powerful ones, has their flaws and weaknesses. Every choice has consequences, and could be the undoing of everything that the heroes are working towards.

Man, I love that book.