In the scene where Will Smith and Jeff Goldblum are being chased out of the alien mothership, Jeff says "Must go faster, must go faster." In the film Jurassic Park, when Jeff is injured, riding in the back of a jeep, and getting chased by the T-Rex, he says exactly the same line; same emphasis, same tone, same everything.
In the scene at the start (look carefully) just before Will notices the alien ship, all of his neighbors are packing up and leaving. There is a mailman delivering the mail to one of the neighbors. Always delivering, come rain, shine, or aliens.
The little boy who plays Dylan co-starred with Will once before. He played Will's youngest cousin, Nicky, on the television show, The Fresh Prince of Bel-Air.
There are several references to other science fiction movies in ID4. When Jeff Goldblum turns on his computer, the computer's voice says 'Good Morning Dave' which is a reference to the film 2001.
The humans are out of missiles in the final battle, except for Randy Quaid, who crashes into the alien main weapon, destroying the ship. A number of problems here. First off, a central control center operator reports all the missiles have been fired, indicating they can monitor all planes. But somehow Quaid's missile escaped their notice. Then no one in the control room seems to know where Quaid came from, which they should know if they were monitoring the fighters. Actually these mistakes stem from the original ending, which involved Quaid arriving to the battle in his biplane with a missile strapped to it, because he was too drunk to be given a fighter. He then flew the biplane into the alien ship because he obviously couldn't fire the missile. But producers felt this was too cheesy and filmed Quaid in a fighter, but chose not to film the control center scenes again.
When the First Lady is hopping in the helicopter to fly out of L.A. , another helicopter is nearby. It flies past a building that has a large IBM logo on it. People are standing on the top of the building, giving the impression that it is one of the first buildings to blow up. Remember that the movie was sponsored by Apple.
The reason for the introduction of the 'biomechanical exosuits' was that actually two alien designs were presented to Emmerich, but since he liked both, the more monstrous design was used for the suits.
-courtesy of The Marlar Sheet
