dncornholio or dnkroz	Toggles God mode, which makes you invulnerable and gives you an unlimited use jetpack.
dnstuff	Gives you all weapons, powerups and keycards, plus full ammo.
dnweapons	Gives you all weapons plus full ammo.
dnitems	Gives you all powerups and keycards.
dninventory	Gives you all powerups.
dnkeys	Gives you all keycards.
dnhyper	Gives you a Steroid power-up.
dnmonsters	Toggles the presence of monsters.
dncoords	Shows you your position coordinates.
dnclip	Toggles clipping (walk-thru-walls) mode. NOTE: Walking outsides the confines of the level tands to kill you, whether you're in God mode or not.
dnshowmap	Toggles the display of the entire level map.
dnscotty###	Level Warp (in the format 104, which would send you to episode 1, level 04.)
dnskill#	Changes the skill level of the current game (where # is the still level).
dnview	Toggles view mode (same as F7 key).
dnrate	Displays the frame rate in the upper left hand corner.
dndebug	Provides a lot of debugging information, could be useful for hunting down problems.

Useless codes:

dncashman	Throws money around every time you hit the spacebar.
dnallen	Gives you the message "Buy Major Stryker".
dnbeta	Gives you the message "Pirates suck!".
dntodd	Gives you the message "Register Cosmo Today!".