NOTE: I am now working with Robsato, please see the original for future updates.
When you do the /dance emote a song will play as you dance. The song that is played is determined by your character model.
You can enable/disable dancemusic in-game with the "/dancemusic on" and "/dancemusic off" commands.
"/dancemusic worgenmerge" Toggles if the worgen human form shares songs with humans [default: shared]
"/dancemusic druidmerge" Toggles if simular druid forms share songs [default: shared]
"/dancemusic showsong" Toggles the display of the expected MP3 [default: off]
To add your songs you will have to place them in the "<warcraft>/Interface/Addons/DanceMusic/Music" folder. The songs should be in the MP3 format.
Use "/dancemusic showsong" before dancing to display file name for current model.
NOTE: To avoid copyright issues DanceMusic is distributed without any songs