Well, first of all, and obviously, any such list (which I did not see on the site)will be noted as much by who it INcluded as well as who it EXcluded. And even if I were to list mine own nominees, as sure as I am writing this at 0748 on Thursday, by noon, I will think of ten more. Having said that and in no particular order...

Woody and Arlo Guthrie
Pete Seeger
Peter Paul and Mary
Joan Baez
Schooner Fare (trio)
the Limeliters
The Kingston Trio
Harry Belafonte
Doc Watson,
Merl Haggard,
Robert Zimmerman
Tom Paxton
Mike Seeger
Peggy Seeger
Kathy Fink
Marcy Marxeer
Craig Johnson
Robert Johnson
John Jackson
Flora Molton
Theodore Bikel

And I haven't even finished my coffee yet!

Saul