Kristen Hersh and the creative commoner.
I was trawling around on ccmixter the other day looking for accapella vocal tracks to sample when I came across the page of Kristen Hersh (Throwing Muses). It seems, being the wonderful experimental soul that she is, she has uploaded a load of bare vocal tracks for the remix community to play with.
For those of you who don't know ccmixter, it's a site, neigh a community, that provides samples for re-mixers and mash up freaks to use legally in their creations. Contributors can license samples and accapellas under the 'Creative Commons' licensing system, a flexible set of legal copyright licenses that grant 3rd parties the legal right to 'play' with the material as opposed to the standard copyright license which allows no freedom to use copy, share or create derivitaves. see www.creativecommons.org.uk/ for all the types available.
Here's a link to Kristen's accapellas on ccmixter and her cash music project page (great songs on here, and all available to remix and mash)
and ccmixter itself.