Duke Nukem 3D Cheats
DNKROZ				God Mode and Unlimited Jetpack
DNCORNHOLIO			Same as DNKROZ
DNSTUFF				All weapons
DNITEMS				All keys and items
DNCASHMAN			Tosses out money every time you press space
DNSCOTTYyx			Warp to level x episode y
DNHYPER				Unlimited steroids
DNSKILLx			Skip to difficulty level x
DNCLIP				No clipping mode on
DNGODLY				God Mode
DNWEAPONS			All weapons
DNITEMS				All items
DNAMMO				All ammo
DNUNLOCK			Open all doors
DNMAJOR				Infinite Jetpack.  You need to have the Jetpack already.
DNUNLOCK			Unlock all doors
DNKEYS				All Keys

Less Useful Cheats

DNDEBUGG			Debug Info
DNRATE				Frame Rate.  25 is good
DNENDING			Ends the Game
DNCOORDS			Show Co-ordinates
DNVIEW				View Mode (same as F7)
DNCOSMO				Register Cosmo today!
DNALLEN				Buy Major Stryker!

NOTE:
When using DNSCOTTY, keep in mind that you have to indicate a level with two digits.  For example to go to Episode 1 Level 2, type in DNSCOTTY102

ANOTHER NOTE:
DNCLIP might crash the game when you walk through a wall into nothingness.  Try not to go off the map.