ohh wow, this topic is a hard one cause there are alot of them for me but ill throw some out there:
i posted earlier a few circa 1960 films that had a huge emotional impact on me as a youngster.
I really liked these as an adult.
The Player. -The Robert Altman film starring Tim Robbins.
The Tin Drum. Based on the Gunter Grass novel and a brilliant adaption of a brilliant novel.
Jean de Florette and Manon des Sources
was fortunate enough to see these (several times) on the big screen back in the day
might have to vote shawshank redeption, or pulp fiction.
The Third Man
The by far best movie ever made is of course Tommy Wiseau's "The Room".
I don't know how there could be a doubt in anyones mind.