I read through this whole thread and some of my suggestions were already said (the Ender's Game Series, anything by Neil Gaiman - I recently read Neverwhere and found it interesting).
If you read the Ender books and like Orson Scott Card, I would try his book called Enchantment. It's based around the Russian Version of Sleeping Beauty, so it's a basically a dark fairytale kind of thing. There's time travel, magic, various immortal deities...
I'm really drawn to dark fairytale type stories, so if you're into that at all, The Book of Lost Things by John Connolly was an interesting read. It basically centers around a boy who is dealing with various traumatic events (his mother's death, his father's remarriage, World War II) and ends up in a fantasy world with various traditional fairytale stories, but with a different/darker twist (ie. the dwarves from Snow White are communists, etc.).
Another book I really liked was Jonathan Strange & Mr. Norrell by Susanna Clarke. It's set in an alternative history of 19th century England, where magic used to exist but has long been missing, until it finally returns with these two men. One of my favorite things about it was the fictional footnotes throughout the whole thing, making it seem like a non-fictional historic novel. Though I will say, I found the relationship between the two men more interesting than a lot of the plot.
Those sound incredibly interesting. *must go to bookstore soon*
The Book of Lost Things is one of my very favorite books. I read it for my contemporary novel project in school almost four years ago and I still think of it all the time, and I reread the tales every so often. I especially like the little red riding hood one. So creepy.
I recently bought a book of retellings of fairy tales by various contemporary authors called My Mother She Killed Me. My Father He Ate Me. I've only read a few, but so far it's so good and interesting.
(Only tangentially related, if you like fairy tales, even just a little bit, the website Sur La Lune is kind of like heaven. They annotate fairy tales with background information and historical context and also collect illustrations.)
Sorry for the thread hijacking.
Anything by Trudi Canavan is good, but the black magician series especially. Daughter of the forrest is awesome, as are the earthsea books by Ursula LeGuin. And Lord of the Rings of course.
Anything by Ray Bradbury or Robert Heinlein is generally great. For dystopia, go for Fahrenheit 451 by Ray Bradbury. For Heinlein, there is Stranger in a Strange Land, Starship Troopers, and The Moon is a Harsh Mistress. I read it in less than a week, it made my top books list. For the record, I hear that the movie Starship Troopers is nothing like the book.
Personally, I'm a really big fan of the older sci-fi. The stories and settings are just pure imagination and always a lot of fun. Arthur C. Clarke is probably one of the greatest scifi writers of all time; read Childhoods End if you get the chance. It's my favorite of his.
Another great one is Philip K. Dick. His book Do Androids Dream of Electric Sheep was the basis for Bladde Runner and it's just freakin' sweet. Also, A Scanner Darkly is a great read (the movie kicks ass too).
And of course there's Vonnegut, you can't go wrong with Vonnegut.