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.