The Shifted Librarian points to RSS feeds from Archive.org. Probably best known as the home of the Wayback Machine, which lets you see web sites as they were during selected points in time in the past, the Archive also houses lots of amazing content, including digital versions of the Prelinger archive, old software, and lots and lots of music.
The RSS feed of their master collection is fascinating. Live performances by Soul Coughing, Gary Jules, Howie Day, From Good Homes, and others are listed right now, and I’m guessing there’s some fascinating other stuff if you dig deeper below the last fifty items.