This is not chant, but it does seem to be an excellent, and beautiful,demonstration of the voice as instrument:
http://homepages.paradise.net.nz/maxq/Vocalise-Rachmaninoff.rm For those of us fuddy duddies who like to be able to discern the words, the absence of any in this piece can be viewed as liberating.

P.S. This piece is not streaming media, so for those of you stuck with a 56k dial-up like I am, there will be around 11 minutes of silence while it downloads, before it starts playing. I still think it's worth it.