http://www.acapellas4u.co.uk/

For acapellas, vocal samples, all original vocal tracks ripped / separated from the music.
You have to become a member even to download 3/month 

This is the .txt list of the songs on the server http://www.acapellas4u.co.uk/lists/acapellas4u_list.txt

jamglue.com is a good site for acapellas and instrumentals, too. You have to register to download there as well but I don't think there's a limit on the number of downloads.

Good Acapella link !
Acapela : http://www.jamglue.com/search?category=All+of+Jamglue&query=acapela&commit=Go
Acapella : http://www.jamglue.com/search?category=All+of+Jamglue&query=acapella&commit=Go

These you can play........as good as on your hard drive ! 

Mostly Rap Commercial tracks though    , but then samples are samples ! Har har!

Supposedly you can make an acapella from any song if you put the original version in audacity, line up an instrumental track so that it's played over top, then invert one of them and the instrumentals should cancel out and you'd be left with only the acapella. It's harder though because it has to be lined up perfectly and the two tracks have to be identical in quality.