Hi
I second the wayside stories, and also the my weird school series by Dan gutman, he also has one about aliens in the same vien. If you haven't seen the a to z mysteries or the capitol mysteries those are good too. My DS also really enjoyed nonfiction and advanced picture books which have lots of information. The magic school bus original pictures books are great and then the chapter books. Howler Karma NASA has a great list and recommendtions - although I can't get my DS into most as he likes futuristic over old fashioned and the language seems to deter him for some reason!

DeHe