SiN

First press the ~ key (just like in Quake and Q2).
Then enter the code:
/health 999 - Health 999
/wuss - All weapons
/superfuzz - God mode
/nocollision - No clip mode
/wallflower - No target

/spawn magnum - Gives the Magnum
/spawn shotgun - Gives the Shotgun
/spawn assaultrifle - Gives the Assaultrifle
/spawn rocketlauncher - Gives the Rocketlauncher
/spawn sniperrifle - Gives the Sniperrifle
/spawn heligun - Gives the big gun from the chopper

/spawn reactiveshields - Gives the ReactiveShield
/spawn rockets - Gives Rockets
/spawn coin - Gives a coin
/spawn health - Gives a healthpack
/spawn cookies - Gives a pack of cookies
/spawn lensflare - Makes a light-effect
(Information from Cheat Machine)