My live pick - Mike Doughty or The Panderers
My dead pick - Johnny Cash
By the way, I saw David Bowie and Imogen Heap both mentioned here. Both of them collaborated with my favorite band, Rustic Overtones, on their album Viva Nueva back in 2001. David Bowie did 2 songs (Sector Z and Man Without A Mouth) and Imogen Heap did one song (Valentine's Day Massacre).