Can anyone recommend a good Teen Fiction book and explain why it's good?

I'm not sure what kind of books you like, but I always recommend the Confessions of Georgia Nicholson series by Louise Rennison. The first book's called "Angus, Thongs, and Full-Frontal Snogging". They're absolutely hilarious, and they just get better with each consecutive book :) They're really about nothing - just a teen girl in England talking about her life. But the way it's written is hysterical. Definitely give it a try :)