Who believes that Robert Plant

Joan Jett and the singer of The Breeders. For male singers Kurt Cobain isn't exactly chopped liver.

Plant. There must be a place near the top for Stevie Winwood.

As far as women singers go, you would need to mention the only woman to sing on a Led Zeppelin album with Robert Plant, Sandy Denny. She was a seminal figure in the British folk music scene.