My son (9) doesn't like reading in general so I have to really put a lot of thought into what will keep him interested.
Anyway today I bought him "The Diary Of a Wimpy Kid" and I've never heard him laugh and giggle so much. He's practically read half of it already, he just can't put it down.
It's really well written, is VERY funny and I think most kids this age could relate to the feelings of the boy who writes it. The "stresses" of school and the ridiculous situations kids that age find themselves in.
This is it on amazon if you want to get a general idea of what the book is about: