Rivers of Babylon
This clip is from an early MadMen episode that featured a campaign for Israeli tourism as a subplot. The song is sung by a Jewish(?) beatnik, at a Village club, but the Babylon the song references can only be understood as the world of the Mad Men themselves.
Historicity: Wiki tells me this song was on Don Don McLean's American Pie album; the MadMen clip, however, is set in 1960.