A lot of cheats:

Start the game using the command line parameter
+set console 1. Then while playing press ~ and 
type cheats on. Then enter any of the following
codes


Cheat:		       Effect:

god                    Invincibility
health #               Health Increased by #
weapon_give_#          Give Weapon # (1-10)
massacre               All enemies on level die
notarget               Invisibility
noclip                 No Clipping Mode
cheats 0               Cheats off
cam_nextmon            Focus Camera on Next Enemy
screenshot             Take Screenshot
cam_nextsidekick       Toggle sidekicks
connect [server]       Pick active server
map [level name]       Pick level
r_speeds [1 or 0]      Change render speed
r_drawflat [1 or 0]    Flat polygon toggle
r_fullbright [1 or 0]  Toggle lighting