The 1948 recording of "Foggy Mountain Breakdown". You might know it as the theme to the 1967 Bonnie and Clyde movie.
I had "The Mercury Sessions" CD of Flatt and Scruggs playing in the background, and when Earl Scruggs launched into his second solo (the up-the-next break) it literally brought tears to my eyes. Wow. His timing is always amazing (he and his brothers used start playing a tune then walk in opposite directions around their house and meet up again still in time) but there's something about the combination of articulation, melody, and time that is briefly a perfect musical moment that transcends 1948 recording technology.
--Nat