The other big code but not really as famous is idkfa which gives you all the ammo in the game and the three coloured key cards.
"WE CAN'T PLAY DOOM, WE'VE HAD OUR SHARE!"
"What you need is a code."
"That's right. iddqd will get you out of those problems you have."
"HOORAY! HOORAY FOR IDDQD!"
"That's right kids. You too can succeed in DOOM. Just type iddqd once you enter the game and the rest is MAGIC."