What's your favourite song with no 'instruments' other than a voice?*

Reason I ask is cus The Futureheads are doing a whole album of it (out April 2nd). Sample track sounds a bit bonkers: http://soundcloud.com/workit/the-futureheads-robot-a

The album also contains some covers, Meet Me Halfway (The Black Eyed Peas cover), Beeswing (Richard Thompson cover), The No. 1 Song in Heaven (Sparks cover) and somewhat predictably Acapella (Kelis cover).

* Got a feeling this might just result in people naming their favourite song on Medulla