With Pocket Tunes, you can listen to SHOUTcast streaming audio on the Treo 600. Stations with bitrates <= 32 seem to work the best. Khaha, the all comedy channel, is a good one. Of course, spoken word content sounds better than music at low bitrates, but even the music sounds pretty reasonable, better than I would have thought.
TreoBits has a list of shoutcast stations that work well on the Treo.
Streaming audio on the Treo is incredibly cool, but it also drains the Treo's battery pretty quickly. Turning off the screen helps.