Nonviolent games for Xbox360 that are still fun

[isiolia]

Second/third/whatever Forza 3. The Platinum Hits version includes a second disc with a boatload of the DLC to boot.

Possibly something like Sonic's Ultimate Genesis Collection, if he likes older games. It's not that expensive, and has enough titles that there's bound to be something in there he'd like.
Similarly, the Dreamcast Collection is not expensive, and all four games would probably suit what you want (Crazy Taxi, Sonic Adventure, Space Channel 5 Part 2, and Sega Bass Fishing)

If you don't feel he'd be turned off by the All Ages vibe, the Lego games are obviously pretty innocuous yet still fun. Plus local multiplayer. In a similar vein, maybe, Marvel Ultimate Alliance 2 or something. Those might work best if he's got an interest in things that they're based on.

If he's an RTS player, maybe Halo Wars - mention due to it being an exclusive. If he doesn't mind them on PC, then maybe he wouldn't mind the style content there either.

[Opa Opa]

Civilization Revolution?

[Gamerforlife]

Rez HD maybe?

[Hobie-wan]

Williams Pinball Hall of Fame.