No one's mentioned Darling Nelly Gray. I don't much care for the tune but it's a classic. My own favorite is "FOLLOW THE DRINKING GOURD" - because it was code for escaping to the north.

It's here (http://www.mudcat.org/@displaysong.cfm?SongID=2072). And a page to "decode" it is here (http://quest.arc.nasa.gov/ltc/special/mlk/gourd2.html).