Heretic

iddqd - instant death - you die on the spot

idkfa - no weapons nor ammo - you lose ALL of your weapons and ammo
for the rest of the game

cockadoodledoo - turn into a chicken - lots of fun!

engageXY - level warp - X is the episode, Y is the level.

kitty - toggle clipping - you can pass through walls. NOTE: you cannot
pick any item up though.

massacre - kill all monsters on the current level - no bad guys to fight!

ponce - full health - recharges your health.

quicken - god mode - you are now invincible!

rambo - all weapons/ammo - idkfa takes ammo away, you can now get it 
back!

ravmap - change map mode - e-mail me and tell me what it does.

shazam - toggles weapon power - does the same as the Tome of Power.

skel - all keys - gives you all three keys. 

ticker - display fps dots - ???

gimmieXY - artifacts - list is below. X is a letter from a to j, Y is a number
from 1 to 9.

A - ring - invulnerability (temporary)
B - mask - invisibility (temporary)
C - potion - ?
D - Mystic Urn - ?
E - Spell book - Tome Of Power
F - Torch - light your way through dark areas
G - Hourglass - time bomb!
H - Eggs - turn monsters into chickens
I - Golden Wings - fly
J - Chaos Device - works only in registered version.