Casablanca (Michael Curtiz, 1942)
Humphrey Bogart doesn't get the girl - when Ingrid Bergman flies off, he's only left with little Claude Rains. But it's the beginning of a beautiful friendship and the film still qualifies as one of the most effective feel-good movies of its era. It was also excellent propaganda, showing the hero overcoming his cynicism and doing his bit against the Nazis. Play it again, and again.