The XBox 360 is fully capable of incredibly high quality, high definition output. It's up to each game designer to take advantage of that detail level. This chart will help you determine which games can reach which levels.

If you don't understand the different TV resolutions, be sure to read my High Def vs Normal Def Explanation

Call of Duty 2 - 480p / 720p / 1080i
Condemned Criminal Origins - 480p / 720p / 1080i
Kameo - 720p
King Kong - 480p / 720p / 1080i
Need for Speed Most Wanted - 480p / 720p / 1080i
Quake 4 - 480p / 720p / 1080i
Perfect Dark Zero - 720p
Project Gotham Racing 3 - 720p