Cube Cheats: GameCube cheats, codes, hints, and walkthroughs
Cube Cheats has a long list of GameCube cheats and codes, organized by game titles. Loads quickly and has a simple, painless design.
Game Winners GameCube codes and cheats
Game Winners has cheats, codes, hints, and walkthroughs for the GameCube and many other game systems. They have a lot to offer the diehard gamer, and it's a fairly nicely designed site.
SuperCheats: GameCube codes and cheats
SuperCheats has a big database of GameCube cheats and codes as well as codes and cheats for other system. If you need walkthroughs, codes, or cheats for the GameCube, this is another good site to try. They also have game trailers for download.
GameCube Cheats
GameCube Cheats has the usual assortment of codes and cheats, plus news and updates in a weblog format. Slow loading, but nice layout.