God of War II

Unlock Arena Of The Fates
Achieve Titan rank on The Challenge Of The Titans to unlock in the Treasures section.
(Thanks to ReDe)

Unlock Challenge Of The Titans Mode
Complete the game on any difficulty mode to unlock in the Treasures section.
(Thanks to ReDe)

Unlock Costumes
Athena - complete the game on Titan mode.
Cod of War - complete the game on any difficulty level.
Dark Odyssey - complete the game on God mode.
General Kratos - collect 20 Cyclops eyes. NB. You have to kill them with a context-sensitive move.
God Armor - achieve God rank in Challenge mode.
Hercules - complete the game on Titan mode.
Hydra Armor - complete the game on any difficulty level.
(Thanks to ReDe)