Beam Me Up, Scotty!: Ripley doesn't say "Nuke it from orbit. It's the only way to be sure," she says "I say we take off and nuke the entire site from orbit. It's the only way to be sure." What's worse is that the line is often attributed only to Hicks instead, who was repeating it in concurrence with Ripley.
Jenette Goldstein (who played Private Vasquez) originally thought Aliens was going to be a drama about immigration and showed up to audition wearing short skirt and high heels. This incident was directly referred to in a crack Hudson makes about Vasquez during the briefing.
Hudson: Yeah, when they said "aliens", she thought they said illegal aliens and signed up!
Creator Backlash: Carrie Henn, who played Newt, has said that she hates the line "They mostly come at night. Mostly."
The Danza: All the actors playing Marines (except Michael Biehn) used their real first names for their characters.
Dyeing for Your Art: All the actors who played the Marines attended a two-week training session with S.A.S. officers, except Michael Biehn, who was a last-minute addition. The other main actors, Sigourney Weaver, Paul Reiser, and William Hope, were deliberately excluded from training, to generate a sense of detachment between their characters and the Marines.
Enforced Method Acting: The scenes on board the Sulaco were filmed last, so that the actors playing the Colonial Marines would have had time to build up a realistic rapport with one another over the course of shooting.
Executive Meddling: The film had many scenes cut from it (though they were restored later in the home video release of the film) that expand upon many plot points in the film. Though some were legitimately dropped (giving away the likely existence of the Queen, for example, or the sentry gun scenes), removing the parts dealing with Ripley's daughter subtracts a major emotional element from the film.
Kyle Reese from The Terminator is the film's supporting hero and he has to help Ripley boss around one of the punks who gets killed by Arnold Schwarzenegger in that film, while Lt. Vukovich is the "artificial person".
Mean Character Nice Actor: Paul Reiser laments having played a character so hateful that his own mother whispered "good" when the Aliens killed him.
One-Book Author: An acting variant. Carrie Henn (Newt), despite winning a Saturn Award for her work, decided not to act again after being bullied due to her role in Aliens.
The Other Marty: James Remar was originally cast as Cpl. Hicks, but James Cameron had him replaced with Michael Biehn shortly after shooting began. A few shots of Remar, mostly from behind, still made it into the movie.
Bishop for Lance Henriksen. Retroactively, yes; but this is so far the only character in Lance Henricksen's career who is a sweet, gentle, polite and kind sweetheart. Everyone else is at best a tired and burnt-out cynic, but as a rule heartless and violent monsters. Until he played the first Weyland years later.
Michael Biehn later said that he almost never got to play heroic characters like Corporal Dwayne Hicks, saying that people who look at him must see something wicked in his eyes and assume there's something wrong with him. These days, he's arguably best remembered for playing heroes like Hicks and Kyle Reese in The Terminator for James Cameron.
Production Posse: Michael Biehn, Bill Paxton and Lance Henriksen are all James Cameron regulars. Jenette Goldstein joined Cameron's regulars starting here.
The picture of Ripley's daughter Amanda was of Sigourney Weaver's real life mother Elizabeth Inglis.
Newt's brother Timmy was played by Carrie Henn's actual brother.
The Red Stapler: Many businesses wanted to buy Power Loaders as forklifts; sadly none were to be bought, since it's a combination of a stunt man sitting in the loader behind Ripley moving the limbs, wires holding it up, and some miniatures work.
Troubled Production: Cameron didn't get along with the English film crew at all, who thought he was a poor substitute for Ridley Scott and disliked him for the simple fact that he was American and not British (ironically, Scott himself would have similar problems when he didn't mesh with the American crew of 1982's Blade Runner). The crew was openly hostile to both Cameron and his then wife producer Gale Anne Hurd, whom they openly mocked by claiming she wasn't the real producer and only got the credit because she was married to Cameron. Actor Bill Paxton later said that British film crew drove Cameron nuts with their "indentured" work ethics, stopping filming just so they could have tea and the like. Things eventually hit their breaking point when Cameron clashed with an uncooperative cameraman who refused to light the Alien nest the way Cameron wanted (Cameron wanted dark lighting to create an eerie atmosphere while the cameraman kept going with bright lighting to show off the intricacies of the set) and finally Cameron, fed up with the bad attitudes of his crew, yelled at the guy "YOU'RE FIRED!" and threw him off the set, which led to the crew walking out, requiring Gale Anne Hurd to coax them back once they had all cooled down. The film went over-schedule and over-budget, and James Horner had barely any time to throw his (very memorable) music score together - to the point that he swore to never work with Cameron again. He recanted later.