The mention of Build-A-Rama came up in another thread and I thought I'd point out that they DO have some little bits for Sci-Fi dioramas (I think even the real-world stuff like oil drums and such can carry over to Sci-Fi too though).
Dunno if you guys have seen them though, so here's pics of the sci-fi stuff. Kinda neat. If you do buy this stuff, push the owner (Mark) to do more Sci-Fi things... Give him ideas, but bare in mind he works in resins which are costlier in general to produce items, and he does this stuff himself so things can get expensive if you go "big".http://www.build-a-rama.com/catalog_sci_fi.shtml
Cargo Crates & A Generator Thingie
I don't mean to do too much advertising for the guy as he's not a sponsor, but I do believe he's good for the hobby... Mention where you came from, push the Sci-Fi stuff and that you'd dig seeing other items... You just might get it (this stuff came about after I hastled him about simply DOING Sci-Fi stuff so he does listen some).
Mark is definitely a nice guy to deal with though, he does great work too... Just look at the more expansive military lines. He even does figure accessories too, so imagine what he could do for Star Wars figures even!