I think (I said I think!) the first French film I saw was Diabolique in college foreign film series. The next French film, I think, was Pourquoi Pas, about a menage a trois, that I saw in 1979, one of my first films in New York. Other films I like include:
Amelie
La Ceremonie
Cyrano de Bergerac
Au revoir, les enfants
La Kermesse Heroique
La Femme du Boulanger
Queen Margot
Going Places
The Return of Martin Guerre