Never a single, so appologies, but I just adore this track from the film Cabaret.
Tomorrow Belongs to Me
I think it is one of the most poignant uses of music in any film. In context, two liberal men are enjoying a glass of wine in the countryside, just outside of Berlin in the early nineteen thirties. The country idyll is interupted by the sweet and gentle sounds of a young boy's song, who it is revealed as the camera pans down, is a member of the Hitler Youth. The song soon turns into a fevered anthem for the gathered National Socialists, who slowly appear on camera, and who rise from their feet to join in the hysterical hymn to racial purity. A glimpse of the horrors to come.