Mentioned only once above, and perhaps lost in shuffle: Joe and Eddie.

I saw these two guys a year or so ago on the old-movie channel (TCM) in an exploitation B-movie caled "Hootenanny Hoot," along with the Brothers Four (not "lesser-known," they were headliners of this film, and not mentioned in this thread), Judy Henske, Johnny Cash, Shep Wooley (who wrote and sang the title song) and a few others.

Joe and Eddie were by far the highlight of the film, for me her and now in the 21st century. Maybe they were ahead of their time ~ very energetic rocking gospel singing with soaring harmonies and minimal accompaniment (just handclaps, and maybe an offscreen intrument or two; J&E didn't play instruments at all.)

Their big number in the film was "There's a Meeting Here Tonight," which I remember from "back in the day," but probably from someone else's rendition. (It was a hit for The Limelighters, who have been mentioned in this thread.)

I did a little internet reasearch and learned that Joe and Eddie recorded a fair number of albums, maybe about a half dozen. A "Best Of" 2-CD set is currently available on CD. Their career was cut short when one of them died young. Couldn't find a cause of death, just a few posted messages wondering how it happened.

Definitely worth a listen for anyone inclined to look 'em up.