Though I like the second film version of Show Boat (1936), the rest of the movie tends to melt away every time I see Paul Robeson sing Ol' Man River. The combination of his rich, uplifting voice and James Whale's stylized direction could make this number a distinctive short on its own.
Robeson would sing Ol' Man River in concert several times over the course of his life-- often changing the lyrics to suit the surroundings or his own personal condition. In his different interpretations, he made that one song function as a downtrodden lament, an uplifting anthem and an angry protest anthem. It is a perfect testimonial to the brilliance of Paul Robeson.