Big Head Mode
Hit R1 - R1 - L1 - L1 - Triangle - Triangle in the pause menu.

Pop Top Mode
Enter Square - Square - Circle - Circle - R1 - R1 in the pause menu.

Skeleton Mode
Hit Circle - Square - Triangle - Triangle - Square - Circle in the pause menu.

Invincibility
Triangle - Triangle - Circle - Circle - L1 - L2 in the pause menu.

All Weapons
Square - Square - Circle - Circle - L1 - L1 in the pause menu.

Infinate Ammo
L1 - L1 - R1 - R1 - Circle - Circle in the pause menu.

First person view in adventure mode
Circle - Triangle - Triangle - Square in the pause menu

Disable Laser Sight
L1 - L1 - Triangle - Triangle - L1 - L1 - L1 in pause menu.

Electric man (in adventure mode)
Square - Square - L1 - L1 - R1 - R1 in the pause menu

Automatic Re-load in shooter mode
Square - Square - Triangle - Triangle - Circle - Circle in the pause menu.

Slow Rockets
L1 - R1 - R1 - L1 - Triangle - Square in the pause menu.

Snake Car in Driving Mode
Circle - Square - R1 - R1 - Circle - L1 - Circle in the pause menu.