Robert Plant and Patty Griffin may or may not be married, but they definitely make a great couple.  Griffin sings in Plant's Band of Joy and Sensational Space Shifters.  Plant lends his voice to Griffin's new song, Ohio.

The acoustic folk song is the first single on Griffin's upcoming American Girl album.  It can be heard here.  The legendary Led Zeppelin singer sings harmony for Griffin on the song.  

Griffin tells USA Today that Plant provided more than his voice for the song, "He came in and arranged it so that it became what it is. He came up with the tempo and the mood on it."