>>>Casablanca
>The Godfather
>Lawrence of Arabia
>On The Waterfront
>The Verdict
>
>How about Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb ... or Battleship Potempkin? Death at a Funeral also is a blast if you haven't seen it.

When Strangelove first came out I thought it would be a classic, but I watched it recently and it didn't wear well with the passage of time.
I'll check out the others- thanks!