The Maltese Falcon and
The Treasure of the Sierra Madre... then I'd have to go with:
Strangelove... and either:
Citizen Kane or
The Godfather... or maybe:
Kane and then Godfather or Strangelove--depending on which one I last saw on TCM.
I dunno, I think Strangelove beats Godfather because when I saw it at the theatre in '64 it changed the way I think about, well, things. Four years later, in '72, Godfather just reinforced my already cynical worldview. Strangelove helped form it. And Chinatown isn't necessarily at the top of the list but it's damn sure in it. Mine anyway.
So maybe I should move Strangelove higher up on the list and ditch Maltese Falcon or Sierra Madre.
I dunno, I'm gonna have to think about this...
P.S. In the unlikely event anyone posts in reply to this, please post YOUR OWN DAMN OPINION, and maybe some explanatory stuff about why you think that way. Don't just post some AFI list or something.