Number one for me is Seksmisja - Polish movie created under communist regime. It's a sci-fi comedy with I watched at least 50 times and it's still good
Second is Alien and sequels. It became part of mass culture. The same on second place is Back to Future and sequels. Star Wars 3-6 is there with Mad Max.
Third place would be Fifth Element, Matrix, Contact, Stargate and Mr. Nobody,