IFYOUTHINKYOUAREHARDENOUGH 	- All weapons and unlimited ammo
COMEANDHAVEAGO 			- All weapons
NADIAPOPOVXX 			- Level Warp (where XX is 01-34)
TAKEONALLCOMERS 		- Infinite energy

Level Select:
In the password box, type G0LVL and the number of the level you want. (e.g. G0LVL5 and you will go to Level 5).

Thanks to Revolution readers Jason Bennet, Christof Sperl, and Pavel Spirine!