Thanks to @foo242 for pointing me to some great stuff on the website of Girl Talk's label, Illegal Art:
- Stay Free's Illegal Art Compilation CD — a collection of tracks relying on uncleared samples, most of which are "officially unavailable."
- Copyright and Music: A History Told in MP3s — a summary of important music copyright legal court cases, with links to the relevant audio.
- An overview of The Grey Album, with links to news articles about the legal battle, and a download torrent file.
- And more...