Velocity Vector
xboxcheats.com is an xbox.com partner site, and has a very complete database of cheats, codes, and hints for lots and lots of XBox games. If you own an XBox and can't seem to finish a stubborn game, xboxcheats.com is one of your best bets.
Game Winners has cheat codes and walkthroughs for a variety of game platforms, including the XBox. They have a lot of info and features for the avid gamer, and it's a fairly nicely designed site. Firefox has had to block some pop-ups for me at Game Winners, though.
boxcheats.com is another good database of XBox cheats, codes, and hints. This one is XBox-specific and deals exclusively in cheats and codes--it's not a forum or review site with a few cheats tacked on as an extra. These guys know their stuff.
Team XBox is a general-interest XBox site with forums, reviews, etc. in addition to the cheats section. I've always found it to be a very information site for XBox owners, although it is rather slow loading.