Casablanca is a favourite of mine, along with Twelve Angry Men for the script, acting and direction. Sunset Boulevard is a belter too, as is Psycho, Vertigo and Rear Window (possibly my all-time fave). City Lights is up there too.
Tonight I watched The Seventh Seal, Ingmar Bergman's playing chess with Death romp. Brilliant. Highly recommended by Tete!
FM I can see what you're saying about quality and impact on the film industry and the artform, but on a shallow level, nah didn't enjoy those I listed before, especially CK.
Wasn't too impressed with The Apartment - I bet you like that one too. Basically I think I need a happy ending otherwise I go away broody and depressed.