Here's my current cheatcode list for IDSOFTWARE games.  What do you think?

Read the DOOM Frequently Asked Questions in 4 files, DMFAQ66A.TXT, DMFAQ66B.TXT, DMFAQ66C.TXT, & DMFAQ66D.TXT.  They should be enclosed with any registered copy of THE ULTIMATE DOOM or DOOM2.  Also look for the FAQ's files online on the BBS hard drive.  In the files, look for cheats and command line parameters for more game options!  Note that no cheatcodes work within a Deathmatch session!

Some DOOM & DOOM2 cheats:
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IDDT		-Toggle full area Automap, full map with monsters
IDKFA		-Killer Freaking Arsenal
IDFA		-Full Arsenal without armor/health
IDCHOPPERS	-Chainsaw
IDCLEV(#)	-Warp to map, in DOOM1 type 1-3 for episode, then 1-9 for level.  In DOOM2, type 01-32 for map level.
IDBEHOLD	-Powerups:  quickly hit I-Invisibility, S-Beserk pack, V-Invulnerability, R-Radiation suit, A-Computer Area Map, or L-Light Amplification Goggles
IDDQD		-God mode, watch attackers in action
IDMYPOS		-Get coordinates of player
IDSPISPOPD	-Walk through walls in DOOM1
IDCLIP		-DOOM2 walk through walls
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HERETIC & HEXEN info:
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Here is the complete (?) list of cheatcodes for Heretic:

QUICKEN - God mode, can not die
RAMBO - Get all weapons
GIMME - Get all the Artifacts (designated a,b,c,...,j)
RAVSKEL - Get a full keyring
RAVMAP - Get an advanced, detailed map
KITTY - Walk through walls
ENGAGE - Jump to another level
PONCE - Get full health
SHAZAM - Power up mode
MASSACRE - Kills all monsters on the level
COCKADOODLEDOO - You get to be a chicken (?)
TICKER - Turns on devparm mode
IDDQD - Commit suicide

DON'T use IDKFA or you will lose all weapons!!!
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Wolfenstein 3-D cheat codes:
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On command line:  wolf3d -goobers
Within the game:
Press Shift-Alt-Backspace
Press Tab-G  health
      Tab-I  weapon
      Tab-   etc.
Type ILM at anytime in the game and you will get full life, ammo, and weapons.  BUT your score will be put down to 0 !!