While playing, type any of these codes and have a blast.

Code        Effect
IDDQD       God mode
IDBEHOLDx   Gain temporary ability. x can be:
              I=invisibility      R=radiation suit
              S=berserk           A=auto map
              V=invulnerability   L=light amps
IDFA        All weapons and ammo
IDKFA       All weapons, ammo and keys
IDCLIP      Walk through walls (toggle)
IDCLEV##    Warp to level ## (01-32)
IDMUS##     Change background music to track ##
IDMYPOS     Display location
IDDT        View complete map
IDCHOPPERS  Get a chainsaw