A list that is constant flux, at this one fixed point in time it looks something like:
-Casablanca
-Annie Hall
-Big Trouble in Little China
-Withnail and I
-Night of the Hunter
Ask again in an hour and it will be different, I already feel bad that Blade Runner, The Third Man, Miller's Crossing, Kelly's Heroes, and Once Upon a Time in the West aren't in that list.
EDIT two minutes later: Two Lane Blacktop? Goodbye Pork Pie? Hellboy? Branded to Kill? The Wrath of Khan? Dead Man? Arrrrrgh! Too many favorites.