Some of the very visible listed below. Did you notice any one of them?
1) Throughout the film, Tony Stark's chest ring can be seen glowing through his shirt except for two occasions when it's suddenly off - after Loki escapes from the helicarrier, and when Loki and Tony Stark are talking in Stark tower.
2) In the scene in Stuttgart, we see a "reserved parking" sign written as "Reservierten Parken". In correct German it would be written "Reservierter Parkplatz".
3) Towards the beginning of the film Steve Rogers is working out his frustrations on a punching bag in a gym. He finally hits the bag so hard that it breaks open and flies against the wall. Watch the chain it was hanging from when he makes the final punch. Despite the force of the blow the chain connecting the bag to the ceiling stays completely motionless.
4) Near the end of the big battle scene, Captain America is winged by a blaster bolt. When he is helped to his feet by Thor, he is holding his side, and there is visible damage to his uniform. In later shots, all evidence of being shot is gone from his uniform.
5) During the fight between Thor and the Hulk, Thor takes a hit to the face. He wipes his nose and gets blood on his finger. The next shot shows his face with a blood drop under the nose, he reaches for the hammer, and when the camera turns back to his face, the blood is smudged without him having moved.