(The title, and the first posts, are amBiguous; is it confined to singers heard in folk clubs, or is it more general? I have taken it to mean people singing folk songs anywhere)
Aubrey Cantwell singing the Nightingale in the Bell in Standlake, c1966.
Seamus Begley singing in Dingle, c 2000.
Gary Davis, Cambridge c 1966.
Martin Cummins singing the Flying Cloud, several places, 60's.
The Watersons, some pub in London 64ish.
Jim Parkin singing Joe Bowman and Follow the Plough, Highwayman, Burro, Kirkby Lonsdale c 1975.