I saw Young Frankenstein and Star Wars in the theater when they came out. To me they are not old. Anyway recently rewatched Once Upon time in the West. I can recommend it.
I also have watched a lot of the old Japanese films like The Samurai trilogy (1954-6) and Harakiri (1962), but my favorite of the genre is The Tale of Zatoichi (1962)
Doctor Strangelove and Andromeda Strain also were worth watching