Unverified. Press the T key to bring up the transmission box and attempt to input the following:

tears - All guns and infinite ammo, reloading still required.
guns - All Weapons.
build - Display build version.
gimmegun turret - Drops current weapon.
armor - Full Armor.
gimmegun assault rifle - Get assault rifle.
gimmegun cannon - Get cannon.
gimmegun dual pistols - Get dual pistols.
gimmegun frag grenade - Get frag grenade.
health - Get Full Health.
ammo - Get Loads of Ammo.
gimmegun missile launcher - Get missile launcher.
gimmegun nail gun - Get nailgun.
gimmegun remote charge - Get pipe bomb.
gimmegun pistol - Get pistol.
gimmegun plasma weapon - Get plasma railgun.
gimmegun shotgun - Get shotgun.
gimmegun submachinegun - Get SMG.
gimmegun proximity - Get trip mine.
poltergeist - Ghost mode.
god - God Mode.
gear - Increased health and boosted reflexes.
pos - Position Mode.
maphole - Skip to next level.
kfa - Weapons + full ammo, armor & health.