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.
Which would go against his belief that there's no need for two composers working in the same film. He only needs an additional composer if he's pressed for time, 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.