When people ask me what is the best movie of all-time is I don't flinch, I just say "Casablanca". It has everything a great movie should have: romance, sacrifice, wonderful lines, a memorable song, incredible acting (even in the smallest roles) and it is one of the few non-film noir movies filmed in the B&W era that I wouldn't want to see refilmed in color (that is in definite contrast to "I Know Where I'm Going!" which begs to be refilmed to show the beauty of its vistas). But the key that makes everything works is the ending. I don't think the ending that exists in Casablanca could be filmed today and though most have seen this movie (or any of its parodies) I don't want to give anything away. But I encourage you to compare the ending of this movie with the endings of other romantic movies such as "An Affair to Remember", "Sleepless in Seattle" and even the most recent animated "Sinbad" movie. Contrast their endings with Casablanca's ending and you see how Casablanca resonates. Many movies have tried to emulate the ending of Casablanca but it never quite rings true because hollywood movies aren't allowed to have this ending yet the only ones who try are either independent or anti-hollywood.