Get Carter. It is so gritty, quirky and the Newcastle/surrounding areas where it was filmed are breathtakingly atmospheric to that era; they leap out of the screen. It's left field in so many ways which make it a stand out for me. I don't know if it's one of those urban myths again but I read somewhere that the original book was set against the background of a fictional Cleethorpes gang world.
I generally like most sci fi films so it would be really difficult to choose one from that genre for me so I will look at non sci fi.
I that case I would have to go for The Shawshank Redemption which is a fantastic film and the performances of Morgan Freeman and Timothy Robbins are outstanding.
I would also like to nominate a recent film which although some people will pick holes in ( because that seems to be the modern way)I thought was one of the best films I have seen and that was 1917 because it was very thought provoking and shot in an unusual way which just really worked.