Ricky Martin & Christina Aguilera "Nobody Wants to Be Lonely"

It was 2001 and the only way to get a copy of Ricky Martin and Christina Aguilera's monster duet "Nobody Wants to Be Lonely" was to buy the song's album or record it off the radio.  Why?  The song was never released as a CD single -- meaning you couldn't go out and buy the song (or in today's terms: you couldn't just download the single from iTunes).  The song wound up being one of the biggest songs of the year and a real head-scratcher as the record companies who would soon lose their grip on CD sales with the rise of Napster and illegal downloads.