Star Wars: A New Hope - although according to one movie buff's blog, this is not a sci-fi film at all but a fantasy film set in space.
The Emperor Strikes Back
Star Trek (2009)
Back to the Future
Signs - what can I say, I love M. Night Shyamalan movies
The Abyss - honestly I barely remember this movie, I need to see it again, but I have a feeling it belongs here on my list.