Enter these codes at the character select screen, to do so press "del" and enter the name.

itsgallus: All Levels All Cities
nineinarow: All Levels All Cities
super well: All Levels All Cities
stevesmates: No Police (don't use unless you know you don't need cop cars)
itcouldbeyou: Gives You 999999999 Points
suckmyrocket: All Weapons, Armor, & A Get Out Of Jail Free Card
6031769: Unlimited Lives
hate machine: Raises Point Values
buckfast: Press the * on the NUMPAD and get all the weapons

                      (for dumb people-you don't put in the colon)      = : - )