Hidden Sarge Skin
Bring down console and type: /model sarge/krusade

In order to use the following cheats in multiplayer mode, the
server must have cheats enabled (ie: /devmap +map [name])

Unlock All Cinematics
From a dos prompt in your Quake3 directory, type:
quake3.exe +seta g_spVideos 
"\tier1\1\tier2\2\tier3\3\tier4\4\tier5\5\tier6\6\tier7\7\tier8\8" 

Unlock All Levels at Skill 1
Bring down console and type: /iamacheater 

Unlock All Levels at Skill 100
Bring down console and type: /iamamonkey 


God Mode
Bring down console and type: /god 

All Weapons
Bring down console and type: /give all 

You can also use the following codes with the /give command: 

allammo
armor
battle suit
bfg10k
flight
gauntlet
grappling hook
grenade launcher
haste
health
invisibility
lightning gun
machinegun
medkit
shotgun

personal teleporter
plasma gun
quad damage
railgun
regeneration
rocket launcher