Well, not strictly the ending, but the scene beforehand, I'd have to go for the duel in The Good, The Bad & The Ugly. Six minutes where the only on screen action is the slight movement of eyes and the twitching of hanRAB, but thanks to great Sergion Leone direction and an outstanding Ennio Morricone score, it makes me heart beat faster than any modern 'action packed' blockbuster.
Oh, would also go for the 'cliff hanger' ending of Italian Job!