The Hunger Games by Suzanne Collins
The Hunger Games is now such a phenomena now that it hardly needs introduction. Katness is cool, if wooden heroine, and the first novel managed to really engage me in her struggles.
Perhaps the most interesting thing about the novels is that they present, initially, as tween fiction. And on some level, they remain that way, by dint of sex or profanity. In fact though, this trilogy is pretty straight dystopian fiction.
And yes, we all know that there was a Japanese film called Battle Royale in which kids on an island kill each other. No, this is not just a remake of that, nerd trolls.