During gameplay select the Electro-Cosh at the weapon selection screen and enter the following codes to unlock the corresponding effect.

Unlock Level Skip:
Press L1, R1, L1, R1, X, X, O, O, Square, O.

Unlock Level Select:
Press L1, R1, L1, R1, X, X, O, O, Square, Square.

Unlock Floating Camera View:
Press L1, R1, L1, R1, X, O, O, X, Triangle, Square.

Unlock Big Head Mode:
Press L1, R1, L1, R1, X, O, O, X, X, O.

Unlock Unlimited Ammunition:
Select the Electro Cosh and press L1, R1, L1, R1, X, O, O, X, Square, Square.

Unlock Invincibility:
Select the Electro Cosh and press L1, R1, L1, R1, X, O, O, X, Square, Triangle.

Unlock Double Damage:
Select the Electro Cosh and press L1, R1, L1, R1, X, O, O, X, Triangle, Triangle.

Auto-Focus on Enemies:
Select the Electro Cosh and press L1, R1, L1, R1, X, O, O, X, O, X.

One Hit Kills:
Select the Electro Cosh and press L1, R1, L1, R1, X, O, O, X, X, X.