Observe sci-fi movies, like Alien(s/3/Res.), AVP, Star Wars, Star Trek, Blade Runner, etc. Tons of concepts to be seen there. Additionally you might hunt some H.R.Giger artwork. Not all his stuff is alien bones, he also did some sci-fi enviroments (iirc he's made some title like New York City, which is quite sci-fi'ish and vast)