Hmmm....I'll add Rufus and Martha Wainwright. They're both probably 'known' (Rufus more than Martha) since they're the offspring of Loudoun Wainwright III and Kate McGarrigle (wonderful singers/songwriters in their own right), and Rufus has some commercial success (even though 'Hallelujah' was somewhat well known because of Jeff Buckley, it became super popular after being featured in 'Shrek'; Wainwright's version isn't used in the movie, but it is on the soundtrack and I believe it to be the best version of the song) with soundtracks, commercials, and by being friends with famous folks like Judd Apatow. Rufus is classically trained, but his parents were folk singers, so his music is an eclectic mix of the two with some pop thrown in. Elton John called him the greatest songwriter on the planet. Martha is less well known but has some incredible pipes. Her most commercial thing ever was providing vocals on a Snow Patrol song (Set Fire to the Third Bar). She has a great, throaty voice and made some headlines a while ago when she did an Edith Piaf cover-song tour (though didn't do any of the hits).
