Get 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"

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

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

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

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

No Clipping Mode:
Bring down console and type: /noclip

Map Mode:
Bring down console and type: /spdevmap map name ( use these maps for Map name- q3dm1, q3dm7, q3dm17, q3tourney2)

God Mode:
Bring down console and type: /god

Get All Weapons:
Bring down console and type: /give all

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

quad damage
all
ammo
armor
battle suit
bfg10k
flight
gauntlet
grappling hook
grenade launcher
haste
health
invisibility
lightning gun
machinegun
medkit
personal teleporter
plasma gun
quad damage
railgun
regeneration
rocket launcher
shotgun