Old Time Music At Clarence Ashley's, The Anthology of American Folk Music(can I count it as one?, if not, I stop here,) The Watson Family, The Country Music Hall of Fame record of the Carter Family and a Mississippi John Hurt album... one of the early ones.
I would hope that there'd be room for a few non-acoustic folk albums. If I was limited to only five, I'd have to deep-six one of the above, and take Braziliance by Bud Shank and Laurindo Almeida.
First response, and there's already thread creep. Sorry about that...
Jerry