Older DS is almost 9 and doesn't care much for fiction and mythological but he does LOVE funny! I second everyone's recommendations!!! The Stink books are funny, an easy read, and there are only 4 of them. Diary of a Wimpy Kid is humorous as well and I think there are 5 books out now and they appeal to different ages.
Hank Zipzer DS read some last year in 2nd grade and this year in 3rd ...