Catching Fire.
And if you haven't read The Hunger Games, by Suzanne Collins, put your computer down right now and go buy it.
I won't say much about the sequel, other than I was really anxious about it because of how amazing the first book was. But it definitely lived up to expectations. Don't know that it exceeded Hunger Games in my mind (not many, if any, books do), but it was still outstanding.
Just wish the third installment of the trilogy wasn't so far away.
