Sidney Lumet directed THE WIZ, the Big Screen Adaptation from the Hit Broadway Musical with Diana Ross, Michael Jackson and Nipsey Russell starring. Nice stretch from his two Pacino films, SERPICO and DOG DAY AFTERNOON. Pacino would have made a great "Scarecrow" wink wink. Of course Michael Jackson played that part
One of the more unusual examples (and certainly one of the more unusual end results) is Popeye, directed by none other than Robert Altman. Harry Nilsson's songs are...interesting, though the most well-known aspect may be the performances of Robin Williams and Shelley Duvall, who look and sound very much like their respective animated counterparts Popeye and Olive Oyl.
Who can forget Vincente Minnelli? Although today Minnelli may be more famous for his long string of top MGM musicals, he was also an incredibly versatile director whose output extended beyond musicals. The most successful examples of non-musical Minnelli films include MADAME BOVARY, THE BAD AND THE BEAUTIFUL, LUST FOR LIFE, FATHER OF THE BRIDE and SOME CAME RUNNING.