Army Men: World War Codes -

Level select:
Go to the main menu, hold R2, then hold R1. Release R2, then release R1. Hold L2, then hold L1. Release L2, then release L1. Then, press Circle, Square.

Invisibility:
Press R1, L1, X, Circle(2), Square(2), R1, Circle at the main menu.

All weapons:
Press X(2), Triangle, Circle, Up(2), Down, Square, Triangle at the main menu.