MJ and Prince would have been amazing as long as it wasn't the shambles that was Madonna and Prince's Love Song.

Madonna and Cyndi Lauper
Madonna and Gloria Estefan
Madonna George Michael/Wham!
Whitney and Beyonce
Diana Ross and Barbra Streisand
David Bowie and Bryan Ferry
Take That and the Spice Girls
Kraftwerk and Pet Shop Boys
Dusty and Liza with Pet Shop Boys

Florence and the Machine and Kate Bush. Make it happen Island Records.

John Farnham and Steve Winwood
Michael McDonald and Tomas Ledin
Patti Smith and Janis Joplin

Beyonce & Adele
The Olly & Pixie one sounds good.