Rikkitic:
Dr. Strangelove. How could I possible forget Dr. Strangelove?
That's actually my single choice if I have to have one, but I agree it is hard to choose.
5th element and Casablanca are great too. And I'd forgotten City of Lost Children - have to find that again.
Another 1990s runner up: Romeo and Juliet - I really like the style of the adaptation.