To enter these codes, choose Credits at the options screen. Then enter the following:

Invincibility: L1, Triangle, Up, Down, Circle, Circle, Triangle, Square, Right, Square
All weapons: L1, Triangle, Up, Down, Circle, Circle, Triangle, Square, Up, Circle
Max ammo: L1, Triangle, Up, Down, Circle, Circle, Triangle, Square, Left, Triangle
Extra ammo: L1, Triangle, Up, Down, Circle, Circle, Left, Left, L1, L2
Easy kills with all guns: L1, Triangle, Up, Down, Circle, Circle, Triangle, Square, Down, R1
Easy kills with other weapons: L1, Triangle, Up, Down, Circle, Circle, Triangle, Square, Down, L1
Puzzles Completed: L1, Triangle, Up, Down, Circle, Circle, Up, Up, Up, Down
Expert mode: Down, Down, Down, Triangle, Down, Down, Down, Square, Left, Right