From Dolphin Emulator:
Dolphin is a Gamecube and Wii emulator. Most games run perfectly or with minor bugs. Games are playable at HD quality, up to 1080p. This is a remarkable feature the actual Gamecube and Wii consoles are not capable of. As an open source project everyone can commit improvements. The code is hosted on code.google.com. Dolphin is actively developed and almost every day new features are added and bugs fixed as well.