Most of the good games on the Xbox and Xbox360 are rated M so I'm not sure which ones you'll be able to fine.
Gears of War and Dead Rising are both good games if you can find them I recommend getting them.
Other then that I would recommend:
- Bullet Witch (I love this game, Its a bit like Devil May Cry and Ghost in the Shell, If you liked those games you might like this one, the graphics are a bit weak)
- Burnout Revenge (Just like the Xbox and PS2 version But a lot nicer looking!)
- Dead or Alive 4 (Great Fighting game)
- Dead or Alive Xtream 2 (This one is an aquire taste, if you like dating sim type games, volleyball, Jet sky and a few mini-games its a lot of fun.)
- Enchanted Arms (an underrated classic Japan style RPG)
- Ninety-Nine Nights (Its alot like Dynasty Warriors, but to me it was better)
- Perfect Dark Zero (Its not a great game, but its fun for a bit, Its worth the Platinum Hit price.)
- Saints Row (A excellent GTA clone, in fact I like it more then GTA)
- Star Trek: Legacy (If your a StarTrek fan this game is a must play, other wise pass on it)
- Tomb Raider: Legend (Just like the Xbox, PS2 and GCN versions, but a whole lot beautiful looking, If you haven't played it play it here!)
- Ninja Gaiden (Yes its a Xbox game but its still great!)
-Castlevania: Symphony of the Night (XboxLive Arcade)
- Teenage Mutant Ninja Turtles (XboxLive Arcade)