I’m tempted to say Twilight just to be an ass.
I agree with Ender’s Game. As for what’s so great about it… read and find out! :D
I also second George R.R. Martin, Terry Pratchett, Neil Gaiman, Vonnegut, Lovecraft, Stephen King and Philip K. Dick. Also, I’m not overly fond of Colleen McCullough’s other stuff that I’ve tried, but I did really like The First Man in Rome.
Other recommendations so far that I have opinions on: Tolkien can be so tedious to read but the stories are wonderful. The Catcher in the Rye is just about the worst fucking book ever written, IMO; you have to read it at the right point in your life to appreciate it, and I didn’t. I love 1984 as much as I hate Catcher. I love The Outsiders almost as much as I love 1984.
I’d recommend Clive Barker. His stuff is so dark and twisted that even the stuff he’s written for kids is more than suitable for older readers. I love his Abarat series.
Christopher Moore. I read my first book by him (A Dirty Job) not very long ago and I promptly hopped on Amazon and added everything else that he’s written to my wish list. Wonderful dark humor. Chuck Palahniuk is also a dark humor writing god.
Joe Hill. (He’s Stephen King’s kid!) I like his short stories a bit better than his longer fiction, but he’s still definitely worth reading. The same goes for Bentley Little (who is not SK’s kid, but SK does like his stuff).
Jim Butcher’s The Dresden Files series is excellent. I can’t say enough good things about it. They’re urban fantasy about a wizard who works with the Chicago PD when supernatural crap pops up. The first book was almost called “Semi-Automagic,” which really captures the essence of it, I think. The plots never drag, the twists and turns are actually surprising most of the time, and the character development over the course of the series is pretty exceptional.
If you’re into comics and graphic novels at all: Watchmen, Maus, Johnny the Homicidal Maniac.
And, of course, you can never go wrong with Sir Arthur Conan Doyle.