Hold down the L and R trigger buttons and enter in the following codes during gameplay. A voice will say 'You cheated' confirming correct code entry.

Unlock All Items:
B, White, White, click Left Analog-stick, press Y.

Unlock Invincibility:
B, White, B, B, Y, Black.

Unlock All Psi Powers:
B, B, Y, White, click Left Analog-stick, Y.

Unlock Full Arrowheads:
A, click Right Analog-stick(Twice), White, Y, X.

Unlock Full Ammunition:
Click Right Analog-stick, A, click Left Analog-stick(Twice), quickly press Y, B.

Unlock Maximum Rank and ALL Psi Powers:
Click Left Analog-stick, Right Analog-stick, Left Analog-stick, White, B, White.

Unlock Weird text
White, A, click Left Analog-stick, White, White, B.