Various cheats

press "T" and type: 

Code                 Result 
JohnWayne            God Mode 
getsome              Full Ammo 
fullmetaljacket      Full Armor 
didnthurt            Full Health 
almighty             All Weapons, Full Health/Armor 
onemanarmy           All Weapons 
rocknroll            Infinite Ammo 
ghost                Spectator Mode 
retreat              Skip Level