I saw Willie Dixon himself on a PBS special "I am the Blues" where he did a pretty darn good version of "Wang Dang Doodle" a few years ago. And I don't know who wrote it but I've heard recordings by Muddy Waters, Willie Dixon, B.B. King and others of "Got My Mojo Working". The best is one I recorded off the radio many years ago. It was done by Muddy, in a live situation, and has to be one of the greatest boogie blues classics.