During game play, press “T” and type in the following codes:

ammo         Full ammo
armor        Full armor 
build        Display Version 
god          Enable god mode
guns         All guns 
health       More health
kfa          All guns, ammo, health and armor
maphole      Beat level
poltergeist  Invisibility 
pos Display  Position 
rosebud      Get snowmobile in snow levels
skillz       Skill Points (Only in Levels 3 & 4) 

Thanks to Revolution readers ^_bLuE_bLoOd_^, BladeRunner12285, Taylor Gatti,

VorteX-real-, and George2k-!