The Ender saga starts with the story of Earth preparing for the second invasion of aliens. The first was barely repelled by an amazing pilot, and the inhabitants of Earth don't want to leave the future of their planet to chance. There is a space station where children are taken to train to be the next defenders of Earth. Ender's taken to train when he's 6.

The Shadow series (also in the Ender's Game storyline) is about another boy, named Bean, who trained with Ender at battle school. I liked this series more than Ender's series (aside from Ender's Game -- it's definately the best).

I would really, really reccomend these books. The only thing is that there are three completely different feels to the books of the series. Ender's Game is concerned with the experiences of the children. Bean's series details the aftermath of Ender's Game. It's got a lot of politics in it, which I normally wouldn't be very fond of, but the books do it so well that I was enthralled the entire time. The rest of Ender's series has a more... mature feel to it. It's a lot about emotions and human interaction.

Anyhow, I'd reccomend reading them in the order of which they're set:
Ender's Game
Ender's Shadow
Shadow of the Hegemon
Shadow Puppets
Shadow of the Giant
Speaker for the Dead
Xenocide
Children of the Mind

You won't regret reading these books. Additionally, if you've got lots and lots of time to kill, try your hand at Atlas Shrugged by Ayn Rand. It's great writing... it just reads SO slow.

What is it they say about silence being golden?