Shareware, v0.91 & v0.92:
To use these codes, just type them in at the console.
(Press the ~ key to get to the console)
GOD God Mode
NOCLIP No Clipping Mode
IMPULSE 9 All Weapons and Keys
KILL Suicide
FLY Fly Mode
MAP E#M# Level Warp

Deathmatch Test:
F10 God Mode
F9 No Clipping Mode (C and D keys move up and down)
F4 See Through Walls
9 All Weapons