The single book that I've probably reread more than any other novel I own (or don't own, for that matter) is Ender's Game by Orson Scott Card. It's a pretty popular piece of sci-fi literature, if that's what you're into.
The novel is set in the distant future, a few hundred years after an alien war. The world-government set up as a result of the war maintains it's authority by keeping it's people in a constant fear of another impending attack by the alien invaders commonly known as "buggers." Gifted children in this world are taken from their parents at the young age of six for military training to defend the Earth from the bugger threat. Card's novel follows one of these children as he spends years of his childhood in "Battle School," a military training facility in the asteroid belt.
I will not give away any further details, but I will say this book is not all about aliens, and laser guns, and space crafts, but follows the deep psychological impacts that are brought on these children that are raised by military scientists on a space station. I would highly recommend this book to sci-fi fans and casual readers alike.
The novel does have a number of sequels and spin-offs, though they are not as popular as Ender's Game, and there have been rumors floating around for years of a film adaptation, but last I checked it is stuck in development hell. A video game based on the battle training which accounts for much of the novel is also trapped in development. I guess the portrayal of Ender's Game in other media can only be described as cursed, though a few spin off comic books have been released by DC Comics.