Covered Up: How many people remember that Whitney Houston's Signature Song, "I Will Always Love You" originated a a country song from an obscure, awkwardly-titled musical? This ended up disqualifying The Bodyguard for a "Best Original Song" Oscar in 1993, despite the song being a massive hit.
Narm: No one was ever going to call Burt Reynolds a great singer. Still, between this and All Dogs Go to Heaven, there's clearly something hilariously off about his singing voice.
One-Scene Wonder: Charles Durning as The Governor of Texas in the film version, especially with his big number "The Sidestep." His performance got the film its only Academy Award nomination.