Hi Mama-
What kind of music does he like? When I was 8 I liked U2 (their older stuff like Joshua Tree, etc), the Newsboys, and of course my mom's rock n roll, which is ancient to kids now.
Now, because I work for a church I really focus on clean lyrics. My favorites are Muse, DragonForce, Red (christian), John Butler Trio, Cold Play, Radio Head, Band of Horses, Fleet Foxes, some Ben Harper, some Amos Lee, Flatfoot 56, The Gorillaz, Jack Johnson,Shawn McDonald, The Postal Service, and I have heard great things about Starlight (I think that's what it's called). Even if you are not a fan of Christian music, it is safe and has a positive message for your kids.(the list goes on and on and on--my hubby is a musician and a music junky). Red is definitely heavier, metal like music, but my momma was a Janis Joplin fan along with other craziness like Simon and Garfunkel, the Beatles, Fleetwood Mac, etc. I don't remember the lyrics to alot of those, but I do remember loving a good beat. Musical soundtracks like The Jungle Book. Any movie he loves, try listening to the soundtrack or theme songs. Also, classical music that isn't typical, like Debussy, anything celtic, native american flute, etc. Oh, the Wicked Tinkers is a drum and pipe band that plays at our scottish festival every year, and they are great. Most of their music is instrumental -- I suggest not purchasing the song wallop the cat, however, you can purchase them from itunes individually, so skip that song (it's traditional, but it's somewhat raunchy in it's meaning) and let him enjoy the rest. There is alot of good music out there. I say, plan a trip to barnes and noble or borders with him (or an hour or 2 in front of itunes with him) and start listening to music samples. You might get a few duds, but you will also get some winners. Good luck!
-E. M