Trivia: Robert Downey Jr. jokingly improvised the line referring to one of the techie's playing Galaga. Director Joss Whedon loved the line so much, he added in the later shot where we see the techie literally playing Galaga.
Trivia: In the final scene of the film, as Tony is unfolding the blueprints for the new Stark Tower, if you look very carefully (slo-mo may be necessary) you can see files with a symbol representing each Avenger in the upper right corner of each file - Captain America's shield, Thor's hammer, etc. The implication being that Tony will build a section of Stark Tower for each of his friends.
Trivia: When Loki is grabbed by the Hulk and repeatedly smashed into the floor, Tom Hiddleston had a rope tied around his ankle which was pulled to achieve the effect. Although, Tom was told that the rope would be pulled while speaking to the Hulk, he was never told when the rope would be pulled so his reaction to quickly be pulled down was real.
Trivia: For the post-credit scene where the group are eating shawarma together, Chris Evans had to wear a prosthetic jaw, because he had grown a beard for another movie and couldn't shave it off. It's also why he's resting his head on his hand through the entire scene, conveniently covering up most of his face.
Trivia: Paul Bettany, who voices Jarvis in this and the standalone Iron Man films, hasn't seen any of them. In an interview he said "This is robbery. I walk in, I say some lines on a piece of paper for two hours, and then they give me a bag of money and I leave and I go about my day...I've never seen one of them...It's not because of any snobbishness, it's just not my thing."
Trivia: Stan Lee had two cameos in the movie but his first appearance was cut. In the scene when Steve Rogers is at the cafe seen in the final fight where he first encounters the waitress who had become infatuated with Captain America after he saves her. Stan Lee basically calls Steve a moron for not asking for her phone number.