The following codes are entered at the 'Extras' menu screen and if they have been entered correctly you will hear Bart Simpson laugh as confirmation. When entering these codes the L/R refers to the shoulder buttons and Left/Right to the control pad.
Unlock Unlimited Power for ALL Characters: Press Triangle, Left, Right, Triangle, Square, L.
Unlock ALL Movies: Press Square, Left, Square, Right, Triangle, R.
Unlock ALL Clichés: Press Left, Square, Right, Triangle, Right, L.