Here's a list of the books that he's written to date, just to get them straight in your mind:
The Underdog, published 1999
Fighting Ruben Wolfe, published 2000
Getting the Girl, published 2001
(published as When Dogs Cry in Australia)
I Am the Messenger, published 2002
(published as The Messenger in Australia)
(Printz Honor 2006)
The Book Thief, published 2005
(Printz Honor 2007)
Underdogs, published 2011
(a compilation of the first three books, The Wolfe Brothers series)
Bridge of Clay, to be published soon hopefully!
Have you read them all? If not, what are you waiting for?