[Note: Sadly, the videos have been removed. I’ll repost them if I can find another source.]
Fans of the movie Seven Brides for Seven Brothers might know that some of the songs are lip-synced. Matt Mattox (the actor who played Caleb) was a professional dancer, but not a professional singer. His part in the song Lonesome Polecat was overdubbed in the final movie. But I found this video where you can hear his own voice in the song:
The actual voice in the movie is that of Bill Lee. What fascinated me was finding out that Mr. Lee also overdubbed the vocals in a song from another one of my childhood favorite movies, The Sound of Music. Here’s the song Edelweiss, as it was originally sung by Christopher Plumber: