NPR use to have a regular, very short, program where the host looked for truly awful recordings. Some of them were collected and offered for sale on CDs (I don't know about current availability). I never got them, even though I am a connoisseur of terrible covers. Some particularly notable examples include a cover of a Beatles song by the sitting president of a South American country; the song so embarrassed the populace that a recall election was held and he was thrown out of office. Another one, which I thought was really amazing was Bob Dylan and Tiny Time doing a duet (they were good friends) of "I Got You Babe."
By the way, I bought that Dolly Parton CD just to have her version of "Stairway to Heaven."
