Must complete the game on certain difficulty levels, Collect certain Items and receive certain ranks.

Effect - Code

Athena - Complete the game on Titan mode.
Dark Odyssey - Complete the game on God mode.
General Kratos - Collect 20 Cyclops eyes. Must kill them with a context-sensitive move. Meaning the O button.
God Armor(The best costume, Doubles all stats) - Receive God ranking in Challenge mode.
God of War costume - Complete the game on any difficulty level.
Hercules - Complete the game on Titan mode.
Hydra Armor - Complete the game on any difficulty level.