Wow! Memory Lane is crowded!
Does anyone remember the Beers Family? Loved their stuff, but very few folks seem to remember them. Robert was the absolute king of the big psaltery.
Liz Dyer -- egad! I could listen to her forever.
Raun MacKinnon seemed a little embarrassed to be reminded a few years ago about the album she did when she was 18, but I still love it.
For "little-known" in the folk venues but magnificent otherwise, I nominate Barry Hansen of the '60s UCLA folk song club, who is now (I believe) "Dr. Demento."
Dave Elson of McCabe's was the first person I ever hear pick Irish jigs on the banjo. Smokin'!
Do the Wurzels count as a folk group?
Probably the most obscure group I ever heard (at either the Ash Grove or the Troubador in LA) was a pick-up band billed as the "Pseudo Mountain Boys". Their mandolinist later joined the Stone Ponies, and their bassist is a theater organist.
I'm sure I'll think of more eventually -- this is a great anti-Alzheimer's exercise for those of us over 60!