Have a saved game file from Ratchet and Clank: Going Commando on your memory card to be able to purchase new weapons.

Challenge Mode

Beat the game.

Discount on Weapons

Have a saved game file from Ratchet and Clank on your memory card.  Then, go to any vendor and then to Gadgetron Employee discount.  You will receive a 10% discount on any weapon.

Get online with the game.  Then, at the Select Login Username screen, press X.  Select the Edit Profile option, hold L2 and press Left (4x), Up, Right, Up, Left.

Play as Nefarious

Get online with the game.  Then, at the Select Login Username screen, press X.  Select the Edit Profile option, hold L2 and press Up (3x), Left, Right, Up, Left, Up.

Play as Old School Ratchet

Have a saved game from Ratchet and Clank on your memory card.

Sly 2: Band of Thieves Demo

While at the Title Screen, hold L1 + L2 + R1 + R2.

Squat Count

While at the Main Menu, highlight the Stats option and press Up, Down, Left, Right, Square.  The amount of squats you have made against an opponent in Multi-Player mode will then appear.

Unlock Double Bladed Laser Weapon

Pause the game and press Circle, Square, Circle, Square, Up, Down, Left, Left.

Alternative Costume for Qwark in VidComics

During a Qwark VidComic, press Up, Up, Down, Down, Left, Right, Circle, Square, Square.