Clear Easy difficulty to unlock the "Old Movie" cheat. This basically allows the game to be played in black and white.
Heal the entire squad
If you die two times and reload when they ask you to, you will be given an option to heal your entire squad.
Old Movie
Beat the game on Normal.
Speed This The Heck Up
Simply beat the game once on Easy. Then go to chapter select and play the very last level on a different difficulty level this will award you with that cheat.
Squad Healing
If you are killed three times in a row, the game will offer you a chance to heal any injuries your squad might have sustained during combat. To expedite this process, you can just throw grenades at your feet.