GameCube (Hardware) Cheats

Alternate starting sounds (Beware, wouldn't work for Site Owner using wavebirds):
Hold Z while the Gamecube logo appears to hear new sounds.

Hold Z then about one second later hold A to hear another sound.

Insert four controllers then hold Z on each of them while the Gamecube logo appears to hear different sounds.
User Cheats by Jondough

Control starting logo:
Hold A while the cube bounces down to form the "G" logo to spin it.

Set system time and options:
Hold A while powering on the system.

In-game reset:
To restart the Gamecube in many games, hold B + Y + Start at the title screen.