Thanks a lot for you answers!
Well,old for me is anything untill 1970 . I'm pretty familiar with 70s 80s 90s + films .
Some suggestions you may or may not see elsewhere:
"The Conformist" (Italy, 1960 or so)
"Rififi" Or any other Jules Dassin
"La Ronde" (Max Ophul's 1950 version)
Anything/Everything by Kurosawa, Mizoguchi, or Ozu from the 50s/60s.
Everything/Anything by Andrey Tarkovskiy, Jan Kadar, and Kristof Kieslowsky (spellings pulled from IMBD, could be off).
"The Third Man"
"Touch of Evil" (Both Orson Wells)
"Double Indemnity" (the "must see" canonical Film Noir, there are more interesting films in the genre, but this one has all the essentials - explore the entire genre if you enjoy it)
Anything made during the German Expressionist or French Impressionist eras (concurrent, silent film days between the wars).
The Umbrellas of Cherbourg, because it is shot/lit beautifully and quite unique.
Since I made some obvious suggestions despite meaning not to, you may as well watch a selection of Goddard, Truffaut, and August Renoir as well. Weekend and Contempt are probably my favorite Goddard and not commonly discussed. The Grand Illusion is really the only Renoir I remember, and outside 400 blows I don't think I saw much Truffaut. But those two are again, the obvious selections.