How's his reading level? If it's average, I'd reccomend Magic Treehouse, because it's fun and educational. I work in a book store, and the popular titles are, of course, Captain Underpants, there's also Geronimo Stilton, Nate thr Great, there's been a Goosbumps series published for the same level. If his reading level is above average, I reccomend The Ranger's Apprentice series. It's kept in sci-fi fantasy, but there's nothing that might be objectionable. They're re-releaseing the Choose Your Own Adventure series. If his reading level is exceptional, I always reccomend Ender's Game. It's a great, fast read and you'll never underestimate a kid again. It all depends on what he's into. Good luck!
:Pagan Mom to Danny and Mal , Wife to Charles Pet Parent to kitty Paige.