Start the game with the -cheats -funlabs command
line parameter to enable cheat mode. Then, press ~ during
game play to display the console window, type one of the following
codes, then press [Enter] to activate the corresponding
cheat function. Note: There is a space before and after the equals
sign "=" when it appears in a code.

Code
God mode godMode = <0 or 1>
No clipping mode noClip = <0 or 1>
Restore health give health
All weapons give weapons
Toggle AI thought aiDisableThink = <0 or 1>
Toggle AI action aiDisableAct = <0 or 1>
Jump to next spawn point revNextSpawn
List all maps spMapList
List console commands help