Star Wars introduced me to Sci-Fi about the age of 9. I remember watching Space: 1999 on tv as a kid, But Star Wars was my first lasting impression. But as good as it was, Serenity, based on the Firefly tv series is hands down my favorite. Fantastic story, excellent action, and Joss Whedon wasn't afraid to kill off favorite characters from the series.
I watched Close Encounters a few weeks ago. Never gets old.
AI was good, but emotionally draining.
I liked Pitch Black in a low budget sort of way, and The Chronicles of Riddick in a high budget with a low budget feel sort of way.
Just saw Avatar. Visually stunning, but I saw that ending about 5 minutes in. Hated that the pilot died, as she was the coolest character IMO.
I'm sure there is more, but for now, its a good start.