Airchecks: Top 40 Radio Repository - RealAudio airchecks from the Golden Age of Top 40 Radio. Good amounts of classic Chicago radio (WLS and WCFL) and even some Milwaukee radio, mostly WOKY, with perhaps mention of WRIT and WEMP... And Detroit, Los Angeles, New York, etc. of course.
WMSE Archives - Also downloadable! Planet Prog at 9PM Sunday night, the Chicken Shack at 9 AM Friday morning, and Jerry Glocka's show Friday at 6 PM are all worth tuning in. If I had a high bandwidth connection, adequate hard drive space AND a CD burner in the same location, I think I'd burn a whole lot of these.