The DOOM/DOOM2 Cheat Code List.

To use one of these cheat codes, simply type in the letters shown
while playing.  Note: The cheat codes do not work while playing
any kind of multi-player game, or while playing on Nightmare
difficulty level.  Except where otherwise stated, all codes work
the same for DOOM and DOOM 2.

Code:          What it does:
idbehold       displays a menu at the top of the screen, select
               on of the following letters: S,V,I,R,A,L:
               (Each replicates a "power up" artifact.  See
               Powerups for details on each item.)
               S = Strength - Berserk Strength  
               V = inVulnerability - Invulnerability Sphere
               I = partial Invisibility - Blur Sphere
               A = Automap - Computer Map
               R = Radiation Suit
               L = Light Amplification Visor
idchoppers     Gives you a chainsaw and prints "Doesn't suck, GM"
               on your screen. 
idclev1        DOOM 1 :  Warps to the Episode (1-3) and Level
                         (1 - 9) you want to play; ie: "idclev38"
                         warps you to E3M8.
               DOOM 2 :  Warps you to the map (01 - 32) you want
                         to play.  Be sure to preface all numbers
                         less than ten with a zero; ie: 1 = '01'.
idclip         DOOM 2 only: No clipping - lets you walk through
                    walls.
iddqd          Degreeless Mode - "god mode", 100% health, you can
                    not be damaged except by:
                    1 - Teleport Frags 
                    2 - A special sector type that ends the game
                        after it kills you (DOOM 1, E1M8).
iddt1          Changes the automap between three states: Normal,
                    All Lines, and All Lines And Things.  (The
                    arrow that is "you" will have "ddt" within it
                    when this code is in effect).
idfa           Gives you all weapons, armor, and ammo, but no
                    keys (added with the 1.4b version of DOOM 1).
idkfa          Give you all weapons, armor, ammo and keys.
idmus          DOOM 2 only: Changes the music to the map number
                    typed in (01 - 32). (This cheat can be called
                    in DOOM, but it will crash the game.)
idmypos        Displays your current position and facing in
                    hexadecimal.
idspispopd     DOOM only: Same as idclip (see note below)

1This cheat code works in Nightmare.

Notes on some of the Cheat Codes:

idchoppers -   idchoppers was named after a game that a friend of
               Dave Taylor's made for a programming competition. 
               Dave's friend, GM, did not feel the game was very
               good as it was turned in before it was completed
               to his (GM's) satisfaction.

iddt -         This cheat code is named after Dave Taylor, who
               wrote the cheat codes as well as the map code for
               DOOM/DOOM 2.

idspispopd -   This unwieldy name was derived from a (then)
               fictitious game called "Smashing Pumpkins Into
               Small Piles of Putrid Debris".  This started out
               as a joke in the comp.sys.ibm.pc.games.action
               Usenet newsgroup during the end of November of
               1993, just before the release of the shareware
               version of DOOM.  Dave Taylor thought it was so
               funny that he included it as a cheat code in DOOM.
               It was replaced in DOOM 2 with IDCLIP, which
               someone on the Net suggested meant "Crushing
               Llamas Into Paté".