Iron Man Codes -

Suits:
Successfully complete the game under the Easy difficulty setting to unlock all suits, including Titanium Man.

Alternately, successfully complete the indicated mission to unlock the corresponding suit.

Classic: Mission 6 
Classic Red and Gold: Mission 9 
Mark 1: Mission 1 
Mark 2: Mission 2 
Mark 3: Mission 4 
Stealth: Mission 11 
Titanium Man: Last mission