Cast Away. And the moment that should have cinched it for him was when Wilson floated away and he was sobbing uncotrollablly. But the fact that he made the movie compelling, despite the fact that he was the only one on screen for something like 90% of the film, is incredible.
I have also come to the conlucsion that in some ways Castaway is Robert Zemeckis's best film. I say this because he took some huge risks and they worked.