Cheat codes for the full version:

macleod - Immortality
keymaster - Unlimited jet pack fuel.
dirtyharry - Unlimited ammo.
buzz - Glider wings
framerate - Framerate counter
phantom - Spy on creatures using the F11 and F12 keys.
snipsnip - Change your player character's gender
gohome - Reset to the start position.
sneakers - Sneaker mode?
thrasher - Thrasher mode - Shows all your enemies on radar.
timewarp - Mission timer On/Off.
weaponcam - Weapon optics display. Follows your fired rounds, like the
cameras in smart bombs.
singletrac - SingleTrac message.
bigears - "Placeholder Sounds" On/Off?
derek7 - Seems to work but no visible results.
warpme - Mission warp? Possibly with an argumnet, as in "warpme dead"?
jumpXXX - Jumps to the level inserted for XXX. In otherwords, "jumpoasis"
jumps to the Oasis level. Known levels that work are: Oasis, Anubis,
Ragnarok, Juggernaut and Dead. Are there maybe secret levels? Like
"jumpsecret"?
bigbrother - Accepted as a cheat code but no visible effect. nocd - Accepted
as a cheat code but no visible effect. baumer - Accepted as a cheat code but
no visible effect. showall - Accepted as a cheat code but no visible effect.

Cheat codes for the trial version:

killer - Happy Trigger Mode
macleod - Invincibility
singletrac - Displays a message from SingleTrac
All Combat Suits/Weapons - In the game menu, in multiplay, click on armory,
then on suit. Click on the bottom suit, which I belive is combat. Then while
it is highlighted press down, (the down arrow), you might take a couple
tries to get it right. It also works for weapons.

Cheat codes for the beta version:

god - Invincibility
tex - Happy Trigger Mode