The Dark Corner (US, 1946)

A noir with Lucille Ball in it? Yes indeed, and not a bad one either, with some very good photography, especially at the beginning, and not the first happily-ever-after noir with an investigator and his hard-to-get secretary.

Strangers on a Train (US, 1951)

I'm going to utter a heresy: Hitchcock was good, but a bit overrated (IMHO).

Le Grand Amour (FR, 1969)

It's slightly pompous and boring filmmaking, but the saturated colouring of the era, and the featured locales make it passably watchable (à la Jacques Tati).