Here are the search results from the YouTubes with pages and pages of backing tracks, meaning tracks with no bass on them for us to play along with.
The styles vary from gospel to funk to blues to jazz so it is pretty good sampling of styles. And, lets face it, sometimes practicing bass without a band around sounds pretty empty. It makes practicing a lot more fun if you can hear what things sound like against chords and grooves.
And if you find one you like and want to keep it, check out http://keepvid.com/ (there are others like this too out there and plug-ins and browser extensions and stuff too). They will download any YouTube clip you want, and they have a little bookmarklet thingy that if you drag it to your browser bar, when you are on a YouTube page it figures out the video and downloads it for you. So you can harvest these things and play them on your 'puter whenever you want. Enjoy.
YouTube Bass Backing Track List