I learned this from alex on game faqs. During the atlas challenge. After the saw room you go up the steps. Kill the first 2 harpies, but not the one below the tower you are bout to enter. Go inside you have to pin him between you and the ladder and kill him with   triangle move so he dies just above the ladder and get caught in the fall. He will bounce for 15 ,20 minutes and give you oooohhh soooooo many orbs..allowing you to get all upgrades.
Beat he game at least once in any diffuculty to unlock the challenge of the gods Defeat all challenges to unlock the following costumes : Ares armor Chef of war (Note: every enemy you defeat his apron gets bloodier) Dairy bastard (Note: In this costume Kratos has unlimited magic) Bubbles Tycoonius
Unlock Making of God of War: Unlocked from beginning.
Unlock Trailers (Teaser and Magic Teaser): Unlocked from beginning.
Secret Message: To get the secret message, complete Spartan mode.
Secret Message 2: To unlock the second secret message, complete the God of War Challenges. Infinite Ammunition: Pause the game and enter the following code: Select, Select, Circle, Circle, R1, R1, Start.
Move Faster: Press Right Analog-stick Forward to roll forward, then press R1 to execute a Hermes Rush shoulder charge before the roll ends. Repeat this to move faster.
Unlock Additional Costumes When you have beaten God of War's Challenge of the Gods five new costumes will be unlocked for Kratos. Not only do they look different, Kratos actually has different attributes for his damage power and defense power and will also collect different levels of health, magic and red experience orbs.
Chef of War: Damage Power 100% Defense Power 100% Magic 300% Health 150% Experience 100%
Bubbles: Damage Power 50% Defense Power 100% Magic 150% Health 300% Experience 100%
Tycoonius: Damage Power 200% Defense Power 25% Magic 100% Health 100% Experience 400%
Dairy Bastard: Damage Power 50% Defense Power 100% Magic 200% Health 200% Experience 200% BONUS: Dairy Bastard has infinite magic supply.
Ares Armor: Damage Power 200% Defense Power 400% Magic 100% Health 200% Experience 200%