Heavy Gear
While holding down the alt-crtl-shift combination type in the following:
hesbackandhesgotagun - Unlimited Ammunition
bedouinprince - God Mode
checkmatein2 - Completes level successfully
I've noted that using these cheats means that your score will not go up. The game realizes that you cheated and does not award success points or add to the number of total kills you have.
Hint - If you go to your combat settings screen you can put an "x" in the Unlimited Ammo and Invulnerability selection and you will actually get credit for your enemy kills, plus it's a lot easier than typing in long cheat codes while holding down three keys. Sometimes I think that entering the cheat code is more of a challenge than playing out the mission.