Jimmie Rodgers was a hugely popular American singer around 1927-1933. He's usually thought of as a country singer, but his music is amazingly eclectic with plenty of roots, yodelling, and some beautiful blues (such as the Train Whistle Blues (30 second sample).
You can pick up a 5 CD box set of Jimmie Rodgers for only $26 on Amazon. Worth the investment. I didn't grow up with this music, but after the success of the O Brother, Where Art Thou? soundtrack I'm getting interested.