Robby,
Gordon Lightfoot, Cat Stevens and Ian Anderson are three of my all-time favourites and I've seen them all in concert.
Ian Anderson's voice is struggling now, but in his heyday, he was brilliant. Here's a live performance of Ian and the band Jethro Tull doing the original "Thick As A Brick":
A few months ago, he released "Thick As A Brick 2: Whatever Happened to Gerald Bostock?" and its songwriting, structure and musicianship make it in many ways better than the original concept album.