I will leave out Star Trek and Star Wars and whether Star Wars can be classified as a true science fiction movie. I guess a lot depends on the definition of science fiction. I do note however many times, it is difficult to differentiate between science fiction and fantasy. Note too both ST and SW do have a lot of influence on me.
Listed below are scifi movies that have influenced me and I would rank them among the tops. It is so difficult to choose only 5.
2001: A Space Odyssey Invasion of the Body Snatchers The Blob The Invisible Man Planet of the Apes
Alien Blade Runner The Terminator Starship Troopers Armageddon/ Deep Impact
Independence Day Jurassic Park Matrix Butterfly Effect Twelve Monkeys