I'm not huge on the whole dystopia thing, mainly because it depresses me, but of the few I've read, I'd definitely say The Hunger Games. The thing about these books is that they aren't shallow, nor do they cater to what the readers might want. They're dark, raw, and hard to swallow, making them ideal for a dystopian book.
Another book I've heard a lot about is The Giver, but I hated it when I read it in school. A lot of people really enjoy it, though. I'm sticking with The Hunger Games, though.