Hit the talk key (T) and type in these codes:

ammo   full ammo
armor  full armor
healthfull  health
gimmegun pistol    pistol
gimmegun dual pistols  dual pistols
gimmegun submachinegun SMG
gimmegun shotgun   shotgun
gimmegun assault  rifleassault rifle
gimmegun semi-auto rifle   semi-auto rifle
gimmegun nail gun  nailgun
gimmegun cannon    cannon
gimmegun plasma weapon plasma railgun
gimmegun missile launcher  missile launcher
gimmegun frag grenade  frag grenade
gimmegun proximitytrip  bomb!
gimmegun remote  chargepipe bomb!
guns   all weapons
kfa    all weapons + full ammo, armor & health
tears  all weapons + infinite ammo
gear   increased health and boosted reflexes
poltergeist    ghost mode
god    god mode
maphole    next level 
build  build version
pos    player position