I'm loving this thread, and I figured it was about time to contribute:
I'll nominate the 1975 recording of Norman Blake, Tut Taylor, Dave Holland, Sam Bush, et al., often referenced as the Hank Deane or HDS Sessions as a worthy contender. See: http://webpages.charter.net/tutbro/tuthds.html. Dave Shreve uses this LP to fine tune VTA adjustments (as discussed here: http://www.tnt-audio.com/sorgenti/vta_method_e.html ), and I've never heard playback of a string bass sound more real than when I had a chance to listen to track 2 "Sauerkraut and Solar Energy" on his setup. The downside: it seems damn near impossible to get your hands on a copy of the CD version, but the LP shows up on auction sites with a fair degree of regularity.

Edited by skeptic - 11/28/11 at 4:53pm