I heard about this on NPR a week or so ago.... apparently someone acquired a buttload of rare live performances from tons of bands, and has made them available on this web site:

http://www.wolfgangsvault.com/Static.aspx?Type=Audio/Radio.htm&CategoryID=RA&LeftNav=Audio/RadioNav.htm#

I haven't dug around for anything specific yet - I just have the "radio" playing their random selections.

Man am I glad Al Gore invented the Internet.