Frank Lambert, Experimental Talking Clock, 1878 (MP3), billed as the world's earliest playable sound recording

The recording has four basic sections:
0:00-0:21 Indistinct speech
0:22-0:33 Lambert clearly heard calling out hours
0:34-1:10 'Silent' period
1:11-1:40 Indistinct speech, possibly reversed
Portions of the fourth section (1:11-1:40) sound as if they may have been recorded in reverse, that is, with the player cranked counter-clockwise.

Further reading:
Glen Sage at at Tinfoil.Com
David Winter's breakdowns and transcriptions here
Story of the discovery: "The World's Oldest Recording: Frank Lambert's Amazing Time Machine" by Aaron Cramer with Allen Koenigsberg: part one, part two