During the game, hit Enter and type csmilton to enable the cheat mode. Type one of the following:

CSYHWH - god mode
CSSTIGMATA - gives you all weapons, powers, items, health, and essence
CSHEALTH - gives you full health
CSGUNS - gives you all weapons
CSAMMO - gives you all ammunition
CSITEMS - gives you all items
CSROSARY - gives you all powers
CSSHROUD - sets your armor to 200
CSESSENCE - sets your essence to 200
CSHALT - stops time from advancing
CSVANISH - kills all enemies on the level
CSHOST - no gravity (flight mode)
CSWIRE - wireframe level map