Ender's Game, by Orson Scott Card, was published in 1985, but don't make the mistake of thinking this book is dated. It is futuristic science fiction and as amazing today as it was back then. The book follows the main character, Ender, as he is sent to a (space station) training school for talented children. The goal is to learn how to beat the alien enemies, casually referred to as Buggers.
I have recently heard that this book will become a movie sometime in 2013, but I can't say that I'm that interested in watching. The book is so complex, switching between characters and introducing new plot twists with shocking revelations that reading it is an intense experience. I'm not sure the big screen can handle that.
There are some graphic violent passages, so I'll keep this recommendation to high school and above. There are also a few sequels to the book which I haven't read. This one was so good, I'm a little worried about being disappointed if the rest can't stack up.