No Treble -
http://www.notreble.com/ - puts up some great stuff. Saw this on their Facebook page... For example, this isolated bass track from the Beatles "Lovely Rita". It's interesting how much he mutes the strings while plucking... makes me want to start finally practicing with a plectrum!
Once on this page, click on the Videos tab to find videos from all kinds of great players.... They just recently listed a couple of isolated bass tracks from John Paul Jones as well.... use the search box to see if some of you favorite players are there!