Bring  up  the  console  with  [~] then type any of the following
cheat codes:

     Note:  To enable the console, add +set com_allowConsole 1 to your
command-line  shortcut  for  the  game. Alternately, you can try using
[Ctrl] + [Alt] + [~] to bring up the console.

Example: C:\Doom3\doom3.exe +set fs_game d3xp +set com_allowConsole 1 

-or- if your game is stored in a folder with a space: 

Example: 
"C:\Program Files\Doom3\doom3.exe" +set fs_game d3xp +set com_allowConsole 1

Cheat code:                       Result:
god                               God Mode 
noclip                            No Clipping Mode
notarget                          Invisibility
benchmark                         Benchmark Game
doomhell                          Skip All Levels
freeze                            Freeze Everything
aviDemo                           Save Demo in AVI Format
gfxinfo                           Graphics Card Info
give all                          All Weapons and Ammo
give keys                         Give All Keys
give weapon_chaingun              Give Chain Gun
give weapon_grenade               Give Grenade
give weapon_pistol                Give Pistol
give weapon_soulcube              Give Soulcube
give weapon_machinegun            Give Machine Gun
give weapon_shotgun               Give Shotgun
give weapon_plasmagun             Give Plasma Gun
give weapon_bfg                   Give BFG
give weapon_chainsaw              Give Chainsaw
give weapon_rocketlauncher        Give Rocket Launcher
status                            Your Game Status
quit                              Quit Game
com_drawfps 1                     Show FPS
toggle pm_thirdperson             3rd Person View
map #                             Load Map #
spawn #                           Spawn # (See List)

Spawn List: (Use with the SPAWN command) 

Flaming Zombie: monster_zombie_bernie
Chainsaw Zombie: monster_zombie_sawyer
Z-sec Zombie with machine gun: monster_zsec_machinegun
Z-sec Zombie with pistol: monster_zsec_pistol
Z-sec Zombie with shield: monster_zombie_zsec_shield
Z-sec Zombie with shotgun: monster_zsec_shotgun
Commando Zombie: monster_zombie_commando
Commando Zombie with Chaingun: monster_zombie_commando_cgun
Fat Zombie: monster_zombie_fat2
Fat Zombie with wrench: monster_zombie_fat_wrench
Bald Zombie: monster_zombie_maint_bald
Zombie with no jaw: monster_zombie_maint_nojaw
Zombie with Wrench: monster_zombie_maint_wrench
Skinny Zombie: monster_zombie_maint_skinny
Zombie: monster_zombie_maint
Zombie: monster_zombie_maint2
Zombie wth Flashlight: monster_zombie_ maint_flashlight
Headless Zombie: monster_zombie_suit_neckstump
Zombie: monster_zombie_suit_bloodymouth
Skinny Zombie: monster_zombie_suit_skinny
Zombie in Labcoat: monster_zombie_labcoat
Zombie Missing Limb: monster_zombie_limb
Zombie: monster_zombie_skinny
Zombie with a pipe: monster_zombie_pipe
Zombie in T-shirt: monster_zombie_tshirt_bald
Zombie: monster_zombie_tshirt_blown
Zombie in Jumpsuit: monster_zombie_jumpsuit
Zombie Eating: monster_zombie_jumpsuit_eating
Archvile: monster_demon_archvile
Cherub: monster_demon_cherub
Hellknight: monster_demon_hellknight
Imp: monster_demon_imp
Maggot: monster_demon_maggot
Mancubus: monster_demon_mancubus
Pinky: monster_demon_pinky
Revenant: monster_demon_revenant
Tick: monster_demon_tick
Trite: monster_demon_trite
Wraith: monster_demon_wraith
Cyberdemon: monster_boss_cyberdemon
Gaurdian: monster_boss_guardian
Guardian's Seeker: monster_boss_guardian_seeker
Sabaoth: monster_boss_sabaoth
Vagary: monster_boss_Vagary
Adrenaline Power-up: powerup_adrenaline
Megahealth Power-up: powerup_megahealth
Invisibility Power-up: powerup_invisibility