Just read the Wikipedia article and the 2011 Slate piece.
... and then enjoy them:
The original, "Mah Nà Mah Nà", from the 1966 Italian movie "Svezia, inferno e paradiso" ("Sweden: Heaven and Hell")
The original 1969 Sesame Street version (video)
The 1971 Benny Hill version (audio only)
The 2011 Muppets Tonight sketch parody, featuring Sandra Bullock
The entry on the Muppet Wiki - many, many differnent versions and references
(Interestingly, the scat sequences actually vary from version to version, borrowing from a variety of musical sequences.)
