Thought it's hardly reaching the masses yet, the Internet radio service
Pandora, which claims to have registered two million iPhone users, is now available for select Windows Mobile Devices. Select handhelds from
Sprint and
AT&T are compatible (click on the carrier for a list of devices).
The beauty of Pandora is that the service generates playlists for you that you're likely to enjoy based on the information you provide about the music you already like. As with all multimedia uses, Pandora's going to be a drain on your data plan so you should choose a plan accordingly.