To date, Rihanna is the one and only artist to be featured on a Coldplay album. Frontman Chris Martin even said, "Rihanna was the only name on the list. It's the only duet we've done and the only one we wanted to do."
Coldplay feat. Rihanna - Princess of China
Aside from "Princess of China," I've been listening a lot to Rihanna's new song "We Found Love." It was released several weeks ago but the music video only premiered a little over a week ago. I already love the song as it is but the treatment for the video gave it a whole other meaning.