Please note VGF's cheat codes have relocated to the main page.
Zatch Bell
Unlock Maestro
Win Time Attack mode 300 times, then deafeat Maestro when he challenges you.
(Thanks to Dkrocks2145@hotmail.com)
Unlock Zeon/Deufo
Complete Zeon's Story Mode (level 35-43).
(Thanks to Dkrocks2145@hotmail.com)