Press (T) to talk and type these:

MPGOD god mode
MPKFA all weapons
MPAMMO full ammo
MPCLIP spectator mode
MPHEALTHY full health
MPWHEREAMI co-ordinates
MPBEEFCAKE increase power
MPKILLMEALL kill all monsters on the level
MPSPEEDUP more speed
MPSTRONGER more strength
MPCALEB change to caleb
MPOPHELIA change to ophelia
MPISHMAEL change to ishmael
MPGABBY change to gabriella
MPBERETTA get the beretta (do twice for dual weapons)
MPSUBMACHINEGUN get a sub machine gun
MPFLAREGUN get a flare gun
MPSHOTGUN get a shotgun
MPSNIPERRIFLE get a sniper rifle
MPHOWITZER get a howitzer
MPNAPALMCANNON get a napalm cannon
MPSINGULARITY gives you the singularity generator
MPASSAULTRIFLE get an assault rifle
MPBUGBUSTER get a bug buster
MPMINIGUN get a minigun
MPLASERRIFLE get a laser rifle
MPTELSACANNON get a tesla cannon
MPVOODOO give you a voodoo doll
MPTHEORB get the orb
MPLIFELEECH get the life leech
MPGOSHOPPING all items
MPNICENURSE +25 health
MPWARD +300 health
MPNEWCROWARD gives ward (25 armour)
MPCARBONFIBER get willpower powerup
MPTAKEOFFSHOES invinsible
MPHERKERMUR triple damage powerup
MPBEANSOFCOOLNESS nice selection of weapons