Well most of the Sci-Fi flicks I've seen have been mentioned by now (which reminds me that I've seen way too many movies, I've seen about 99% of the films mentioned), but some that I haven't seen on here yet are Short Circuits 1 & 2, movies about a robot that's come to life after a freak accident and has to run from the autorities that want hm back (he's designed as a war machine).
On the Japanese side there's Casshern(live action), which is visually stunning (according to most who've seen it, I was not all that impressed with some parts to be honest), but depending on the cut the story can apparently be quite a mess (you can also watch Casshern Sins, which, though an anime, is not your run of the mill action anime(completely different story/ main character though, only some visual/naming consistencies(the main character is named Casshern and looks similar, there are other Cassherns too)).
Another unusual anime is Voices of a Distant Star, which is a short film about two people trying to remain in contact through texts which take longer to arrive the further one of them travels (it might not sound Sci-Fi like, but one party travels through space to take part in a war with an alien species).
Heh, even though you said you didn't want to watch anime, half of what I suggested is anime. Still CS was more of an afterthought due to Casshern (which is not an anime), and Voices is rather short (my copy is 25 min.) so it might be okay. (Interstella is great by the way, if only for the soundtrack (which coincidentally
is very important in the movie))