Music: Covers With Original Artist

What cover versions have the original artist doing backing vocals/playing an instrument?

• All of The Smiths appear on Sandie Shaw's version of "Hand In Glove".
  
• Tom Petty sings backup on Johnny Cash's cover of "I Won't Back Down"
  
• Jane Birkin covered Roxy Music's "In Every Dreamhome A Heartache" as a duet with Bryan Ferry.
  
• When Whitney Houston covered Annie Lennox's 'Step by Step', Annie provided the backing vocals.