Brownie McGhee, "Sporting Life Blues." That's the one that does it for me. Gram Parsons, "Wheels," is a very close second. I think it's the progression to the tonic 7th chord in both of these. The theme music for Kevin Brownlow's tv series "Hollywood: The Pioneers", also, the passage that's playing when you see the shot of Clara Bow and the dog.

Happiest? Anything by the Skillet Lickers or the Allen Brothers.