The human vocal tract is well built for maximizing the number of different sounds it can produce. Particularly notable is the way the tongue can move freely in the mouth and the modifications that support the abillity.
I'm always happy when there is a new paper by Bart de Boer. He studies the mechanics of producing speech sounds, and in the next issue of the Journal of Evolutionary Psychology he has a review paper on the human vocal tract (draft here). As it is available online, I will limit myself to reporting data that caught my eye: