Press [F10] then type:

Code - Result
godgames - God Mode
thunderstorm - Rains Outside
snowstorm - Snows Outside
bighead - big Head Mode
winblows - All Weapons and Ammo
skeletonkey - Gives Skeleton Key
moreammo - Gives More Ammo
goremode - Toggles Gratuitous Dismeberment
burningstake - Gives Flaming Tip Arrows
freezer - Toggles Enemy Freezing
ifarted - Gas Mask for Stranger
healme - Restores Health
silver - Gives 500 Silver Bullets
aqua - Gives 500 Aqua Vampire Bullets
mercury - Gives 500 Mercury Bullets
oldhat - Stranger Wears Alternate Hat
goldmode - Tells You "buy FLY!"