For all the talk of Giger being a unique genius (and he is) I don't think Ron Cobb gets enough credit for the unique look of the Aliens films. I think it was a brilliant idea to have basically two designers, one to do the alien stuff (Giger) and one to do the earth technology (Cobb). This really created the proper contrast between the two cultures.
Surprisingly, very few films have used this good idea, and instead have one or two artists just work on everything, with no division. One of the exceptions was the Lord Of The Rings series where they had Alan Lee design most of the "good" stuff and John Howe design most of the "bad" stuff. But that was something that really evolved more during preproduction and wasn't part of the original strategy the way it was on Alien.
Then again, the strategy in the design for Alien of having Giger only do Alien and Cobb do human stuff may have grown out of the fact that Giger's stuff just WAS alien. There was really no way Giger could design familiar Earth technology, even if he wanted to. It's just not in his DNA.
Ron also did the design work on Conan and did some of the creatures from the Star Wars cantina (Hammerhead comes to mind)
I'm sure it's all old news to you guys, but here's the wikipedia page about Ron Cobb:
http://en.wikipedia.org/wiki/Ron_Cobb