Catching Fire, right away. There is always that fear that the sequel won't be as good as the original (Hello, New Moon), but that's not the case with this novel. Right from the start, Suzanne Collins continues the action and unbelievable story.
I'm going to give away a bit of the plot, SO STOP READING IF YOU DON'T WANT SPOILERS. Katniss and Peeta are sent back into the Hunger Games, this time against all the other former victors. This was a turn of events that was so shocking and awful to me. The most touching part of the novel was when Katniss realized that no matter what happens, her children are doomed to the Hunger Games as well. My stomach dropped when I read that section.
OK, YOU CAN READ AGAIN. Suzanne Collins doesn't let up in the sequel. I didn't know whether to savor it or rush like I wanted to. The final book in the trilogy is due out on August 24th and everyone at school is already salivating. Might as well pre-order it now!