There seems to be a lot of confusion in this thread between folk singers and singer/songwriters. I'm not knocking the later group. Some of my favorite people are in this catagory: Bill Staines, Chuck Brodsky, et al. I like Arkie's list, especially the Para's, Michael Cooney, and Gordon Bok.
Also, this list reflects most those artists who have lables. There are a host of other performers who are not well known because they don't have a contract with a company that can distribute their material. I would add Judy Domeny Bowen to the list of singers of old folk songs.
It is interesting to see some of the names on these lists. There are a number of them that I am not familiar with. Others that I would disagree with, and many I think are fantastic. As some above have said, "...in the eye of the beholder."