One of the most apt URLs to date:
http://awesometapesfromafrica.blogspot.com/
The gist: music from cassettes produced in Africa from all over the continent, including Ghana, Egypt, Morocco, Senegal, Mali. Many different styles, many different countries, much amazing music.
I won't lie: I have no idea about the legality/rights of these mp3s. It's hard to know what is old and out of print v. what is simply of low production value. I emailed the site owner, but I have not yet received a response.
What I can say, however, is that there is some incredible music on this site that I think many of you folks will appreciate. Mo and I have only had a chance to listen to a handful of the tunes (there are hundreds), but I've already fallen instantly in love with Karamoko Keita (http://awesometapesfromafrica.blogspot. ... ourou.html). Tomorrow I'm hoping to get the chance to listen to the tune that the reviewer has asterisked as "holy shit."
Killer stuff. I highly recommend checking it out.