Press "~" to open the console and type any of the following commands:
Code - Result:
horsey - Activate Cheat Codes
god - God Mode
teamgod - Team God Mode
amphibious - Breathe Underwater
fly - Fly Mode
ghost - No Clipping
loaded - All Weapons
invisibile - Invisibility
killpawns - Kill Computer Players
killenemy - Kill All Enemies
killcars - Explode All Cars