Orson Scott Card's Ender's Game is awesome. Read the rest of the books in the series only if you're a hardcore Ender fan. They're still good, but a little anti-climactic for me, personally. If you've already read the whole series I recommend that you read both Ender's Game and Ender's Shadow (parallel novels) in tandem. It's awesome to see the same story from 2 different points of view. You get to see how human these kids really are, no matter how high their IQ.

ANY of Isaac Asimov's books are good. No matter how many times I read it, I'm still amazed at how seamlessly Mr. Asimov puts things together.