For my money, hilbilly soul (meaning old-timey Appalachia) doesn't go any deeper than Ralph Stanley and the Stanley Brothers. He sings hill music the way God intended it to be done and sounds like he was singing about Kentucky even before Daniel Boone and Davy Crockett got there. For the record, I'm also a huge fan of Jimmie Rodgers, (who learned a hell of a lot from Blind Lemon Jefferson), the Carter Family, The Louvin Brothers, The Sons of the Pioneers, Flatt & Scruggs, much of Bill Monroe, The Light Crust Doughboys, Hank Thompson, George Jones, Patsy Cline, and Lefty Frizell, among others.