Continuity mistake: When Hulk throws the chunk of sheet metal at the helicopter, it glances off the rotor housing (taking a ragged piece with it.) When the chopper crashes, however, the propeller comes off with a perfectly clean edge, as if the projectile had sheared completely through the base.
Continuity mistake: After the first time we see Bruce transform into the Hulk, he has hitched a ride with the elderly man. You will remember he has 3 1/4 length pants on with a few rips. It cuts to a quick clip of him walking up the road but this time he has full length pants on. They switch back to shorter length pants straight after.
Revealing mistake: In the beginning of the film, Bruce Banner's hair is a dark brown and looks natural. When he is doing the anger control exercises, he is obviously wearing a black wig which is not natural looking at all. This happens a few times during the movie - it switches from his natural hair to the very dark wig. And at times, even his eyebrows look much darker and thicker.
Factual error: When Blonsky is seen wearing the American Class A uniform, it's visible he has not shaved his face for days. Quite unthinkable for the military - be it American or British. If he had time to change from his BDUs to the Class A uniform then he would have had time to shave as well. Soldiers in Iraq aren't even excused from shaving daily unless they have a medical condition that prevents them from shaving.
Revealing mistake: In the scene where Bruce is in the helicopter hearing about the other "hulk", the camera is the only thing being moved around to simulate a shaky helicopter ride. The equipment nor any of the actors inside the copter are moving around or stabilizing themselves according to how bumpy the camera movements are making it out to be.
Factual error: All of the soldiers in the movie are wearing the Battle Dress Uniform, but at the time the movie took place (around the same time as the first Iron Man) that uniform was already phased out and replaced with the Army Combat Uniform. Also, all of the soldiers had their name tags on the left side of the uniform, where the U.S. Army tag is supposed to go, instead of on the right side.
Factual error: General Ross and Blonsky are shown in their Class A uniforms, and both of them are missing their U.S. insignia on the collars. Also, General Ross is shown wearing the infantry cross rifles branch insignia on his collar, but as a general officer he would not wear a branch insignia. I could give Blonsky a pass since he's a British officer wearing an American dress uniform for reasons not explained onscreen, but Ross should have known much better as a general with decades of service.
Continuity mistake: When Abomination pins Hulk to the wall, and Hulk starts to push back, at first, when the camera view is level with their heads, Abomination's left hand is grabbing Hulk's right forearm. But when the camera view lowers to their abdominals, Hulk's right hand is grabbing Abomination's left forearm.
Factual error: When Bruce and Betty are attempting to drive into New York, they get stopped at a police roadblock at the tunnel entrance and start walking instead. When we see them crossing a bridge, a sign says "No Wake - Speed Limit 9km\H. Being in the United States, this would be miles per hour or knots, not kilometers.