My ds was the same way; humorous books always hit a much bigger note with him than any other kind, except: books with PICTURES! Combine these two and it's almost always a winner for him.
you might want to check out the manga graphic novels, there are several series that are good for kids:
Hikaru No Go is a great one about a kid possessed by an ancient Go playing spirit guiding him in his pursuit of becoming a pro Go player.
as for books, previously he was a huge Captain Underpants fan. Now he loves the diary of a wimpy kid books, Origami yoda books, enjoyed 'Science Fair', and is currently checking out the series 'Mad Scientists club' suggested on this forum.
