Big Head Mode
Enter NickWest as a code.

Unlimited Ammunition
Enter MERCENARIES as a code.

Authentic Mode
Enter SWEDISHARMY as a code. 
This is a more difficult version of the game, without the HUD.

Army Version 
Enter HA2P1PY9TUR5TLE in cheat codes.  

Concept Movie 
Beat the game on any setting to unlock a concept cinema.