This is a classic song that I posted once in the songs thread before, but I don't think there's any harm in posting it here as well.
It's "Unga Ponnaana Kaigal" from
Kadhalikka Neramillai (1964), a song that I just randomly encountered once while I was in Kerala watching TV because I was tired out from visiting distant relatives and bored.
http://www.youtube.com/watch?v=oscylVvZ-w8