PC:
The following codes are entered from the Player Select screen by renaming your character to the code you want to use.  After entering the code you want to use you can then rename your character to another code, which will enable multiple cheat codes, or you can rename your character back to whatever you want.
   Cheat Code Effect
itsgallus All Levels All Cities
nineinarow All Levels All Cities
super well All Levels All Cities
iamthelaw No Police
stevesmates No Police
itcouldbeyou Gives You 999999999 Points
suckmyrocket Start With All Weapons & Powerups
itstantrum Unlimited Lives
6031769 Unlimited Lives
hate machine Multiplier Raised to 10
buckfast Press the * on the NUMPAD and get all the weapons
callmenigel Press the * on the NUMPAD and get all the weapons
porkcharsui Diagnostic Mode (More Info Below)
iamgarypenn Enable Extra Offensive Language Mode
iamnotgarypenn Disable Extra Offensive Language Mode
Heart of Gold View All Cutscenes