Hold L2, enter cheat, then release L2.

Invinciblity
Square, circle, left of d-pad, left on d-pad, circle, square

Infinite Ammo
left on d-pad, circle, R2, right on d-pad, R1, square

Infinite Mind
R1, R2, circle, right on d-pad, R2, circle

Aware Like A Fox
Right, Square, R2, R1, Right, R2

Nobody Loves You
Right, R2, R1, Square, Right

Mmmm Brains! (Must be entered on Mothership)
R1, R1, R2, R2, Left, Right, Left, Right, R2

More Upgrades (Must be entered on Mothership)
Square, Circle, Left, Left, Circle, Square