Depends on when and what sort of enviroment.
my most memerable is definetly Alien!
When it came out it was a total new idea, amazing scenery and artwork from Giger, scary even though you didn´t see much of the alien, brilliant realistic acting and a women heroin. This movie had everything imo.
Modern Movies, well I´ll go for Pitch Black, dunno why but I just liked it.
hmm well lets see.... I have loads of favorites actually, so give me some time to shave off the right one from the following nominees:
The Matrix
The Matrix: Revolutions
Children of Men
Star Trek: Generations
Star Trek: First Contact
Chronicles of Riddick
Star Wreck: In the Pirkinning
Equilibrium
War of the Worlds