To use these cheats press the ~ button during gameplay then type in the code of your choice below (All of these codes are single player only but turbo works in multiplayer):

Code: Effect
turbo: makes better graphics at the expense of game speed
sunandsteel: Reload all weapons
diewithyourbootson: Unlimited ammo
thetrooper: Invincibility
stilllife: Invisibility
revelations: 8 laser designator shots