WAMU is offering an MP3 stream of their live broadcast.
I've been playing around with Airport Express's AirTunes, and I've found that one of the local public radio stations in the Washington area, WAMU is offering a streaming MP3 live feed. All I had to do to play it through iTunes was click on the MP3 tab next to “Listen Live” on their website. From there, it streamed without a problem to my remote speakers. I'm not finding many public stations doing MP3 streams, most are using Real for their streaming (which doesn't work with AirTunes.)