If you liked Absolutely True Diaries of a Part-Time Indian by Sherman Alexie
--thanks to the folks at LM-NET for these suggestions

The Outsiders by S.E. Hinton.

humor with some seriousness....try these titles:
Killer Pizza by Greg Taylor
Hold Me Closer Necromancer by Lish McBride
Monster by Walter Dean Myers
Spanking Shakespeare by Jake Wizner
Stuck in Neutral by Terry Trueman.
Uglies by Scott Westerfeld

Swim the Fly by Don Calame
Unwind by Shustermann
The Juvie Three by Korman.

Nonfiction:
How they croaked, which is all about famous people like king tut, beethoven and president Garfield and the truly gross details of how they died. It's so funny and illustrated with great drawings. I recommend it all the time, and I just loved "Absolutely true diary." I think they would really like it.