For all you Doom players out there who have been wanting a hint code like
"MLI" for Wolf3D, here they are, compliments of me, Brian Ellenberger.

Just type them in while playing.  You don't even need to hit them all at the 
same time.

Just type it in again to reverse what you did.

"IDDQD"-Total Everlasting Invinsibility.

"IDKFA"-Full ammo, health, and armor.

"IDSPISPOPD"-No clipping-In other words, you can go through the walls.

"IDBEHOLD"-For the verious tech weapons you can get, like Infrared glasses, 
rad suits, etc.  Once you type in the code, then type either "S", "V", "I", 
"R", "A", or "L", depending on what you want.

"IDCLEV"-Warp to any level.  After typing in the code, just type what episode 
and level you want to warp to , like "IDBEHOLD, 1, 9" to get to the last level
in the shareware edition.

"IDMYPOS"-Map position in X-Y coordinates (not very useful)

"IDCHOPPERS"-Get chainsaw.

"IDDT"-Increase map detail.

Well, these are all the codes I've found.  I hope there useful!