Top 5 is realy tough to choose from so many greats.
1, metropolis, still as relevent and important a movie as when it was made in 1927
2, Alien, gritty, great visual style and fantastic story, and the best monsters in movie history
3, Blade runner, deep complex diologue, amazing visuals and compelling characters/story.
4, Akira, cyberpunk sci-fi at its finest and very influential anime movie.
5, Terminator, all round great movie.