Out of left field
A Face In The Crowd - A 1950s movie starring Andy Griffiith prescienctly dealing with the effect of television on the American public.
Had a huge effect on me and while it is not that well known it probably sticks in the mind of those who saw it.
Others would be To Kill A Mockingbird, The Godfather trilogy, The Wizard of OZ, Schindler's List, D Day, The 6th of June, The Manchurian Candidate and many others.
I couldn't single out one flick that stands out but the overall effect of movies on the world is huge.
