My immediate thoughts were:

Pete Seeger
Ronnie Gilbert
Fred Hellerman
Thoedore Bikel
Glenn Yarbrough
Alex Hassilev
Ernie Sheldon (Lieberman)
Chad Mitchell
Mike Kobluk
Joe Frasier
Judy Collins
Joan Baez

And, of course, Mudcat's own Frank (Stringsinger) Hamilton.

Just to name a few...

This could definitely turn into quite a list!

An earlier post by MtheGM mentioned Heather Wood. Happily, Heather was in attendance last night at the final (temporarily) Chantey Sing at South Street in New York City. She was in great form: she lead a song, and participated in an impromptu dance with several of the ladies. It was so nice to see her there.