This one is fairly non-obvious, and also something of a Mythology Gag. In the 2010 game Dr. Groves is voiced by the same guy who played Lt. Gorman in Aliens. You can only tell by looking at the credits, though, as he uses a completely different accent. He also voices both the Alien and Predator.
Given the name appears as such in the credits, "Grid" for the head Xenomorph in the first movie. Also, the lead Predator is listed as "Scar".
Two from Aliens vs. Predator: Requiem...
The "cleaner" Predator was nicknamed "Wolf" - a reference to Harvey Keitel's similarly employed character in Pulp Fiction. The crew also called the Predalien "Chet" after Bill Paxton's character in Weird Science.
A very early script of the first film would have had the film take place in the same timespace as the Alien trilogy, complete with a Ripley expy!
Jerry Goldsmith and Alan Silvestri were planning to team up for the first film's score but Goldsmith's battle with cancer (and eventual passing) prevented the pairing from occurring. Which would have gone against his belief that there's no need for two composers working in the same film. He only needed an additional composer if he was pressed for time (as with Star Trek The Motion Picture and Air Force One), and he couldn't make the deadline. "How many composers does it take to screw a light bulb?", indeed.
Toilet Humour: Believe it or not, Aliens vs Predator was dreamed up when one of the creators, who was struggling to come up with ideas for a new comic book series, decided to take a bathroom break. During his break he realized that Fox owns both Alien and Predator franchises. He came running back to the room with all of his colleagues shouting "ALIEN VERSUS PREDATOR!" Yes, that's right; Av P is the result of a really good poop.