Doom

Normal cheat:
During play, type the codes with the keyboard.
You don’t need to hit [Enter] after the code.
After entering, a message should be displayed at the
top of the screen telling which cheat mode was activated.
iddqd     Degreelessness mode (God mode)
idkfa     Very Happy Ammo (full ammo, 200% armor, all weapons)
idspispopd No clipping (you can walk through walls)
idbehold   Displays menu (followed by S, V, I, R, A, or L)
idclev     Warp (add episode and level number)
idmypos   Displays your coordinates in hex
idchoppers Gives you the chain saw
iddt     Toggles Automap between normal, full,  and full with objects
        (enter when looking at the Automap)
Junkies cheat:
Iif you are really addicted and haven’t got enough with the previous
cheat, here are more goodies. 
You get :
- A demo-movie showing how to get to a   secret hidden level
- Instructions on how to use the infamous command-line parameters
  and how to build   your own Doom-virtual-reality-setup !
It is a all in the included file.