Sci-fi: I'm not going to repeat what has been said in
here. Just read the thread.
Post-apoc.:
more SF-like:
A boy and his dog - one of the inspirations for Fallout games. Fantastic internal consistency.
Mad Max series - like you don't know these.
Delicatessen - french oddball cannibalistic drama/comedy. Happens to be set in a post-apoc world that we never learn anything concrete about. Superb.
Hardware - a bad film. B-movie killer machine thriller. Still, some interesting scenes and well-chosen music manage to sneak a bit of that tasty post-apoc atmosphere.
Planet of the apes(1968) - classic is classic. I like how minimalistic and meaty it feels when compared to the standard today's SF fare.
Six String Samurai - a katana-brandishing Elvis-incarnation defends Rock'n'roll from demonic
Slash and the Russian Army with the power of his moxie, martial arts and some mad tunes.
Sexmission(if you can find english subtitles) - a Polish oldie comedy. Two last men on Earth wake up from cryogenic sleep to a totalitarian world run by female clones.
Le Derniere Combat - I don't actually know anything about this one, apart from it being post-apoc, French, having young Jean Reno, and being in black&white. I've been meaning to watch it for a longer time, but can't get around to doing it.
more-pseudodocudrama-like
Threads - British no-punches-pulled portrayal of nuclear exchange aftermath. Scary as hell.
The day after - the weakest of the three, we follow several people during and after full-scale exchange in USA. Some cool moments, but often feels cheap.
Testament - USA again. Bombs drop some distance from the town we're in and the people are trying to cope. Some interesting take on coming of age story amidst a slowly deteriorating society.
Gangster'y:
Once upon a time in America - Sergio Leone's crime epic spanning some 40ish years from 20s to 60s. It's Sergio Leone's and it's epic. It's doubleplus good.
The Untouchables - Costner and Connery are catching De Niro's Al Capone. Not extraordinary, but very watchable nonetheless.
Scarface - seconded. Classic Al Pacino in a classic film.
The Godfather series - do I have to explain?
Forrest Gump-like and Shawshank Redemption-like:
Too vague a category. Need more constraints.