The Cooperative Children's Book Center (CCBC) at the University of Wisconsin-Madison is a GREAT resource for finding ideas for what to read next. You can search by author, by theme, by age level, etc.
Take a look at their suggestions for Middle and High School age readers. You just might stumble onto something great! If there is a title you want, we can ask Mr. Liljedahl in our library about how to find it--or include it on our book wish list when we start to ask for book donations in our community.