Lucas Gonze, Jim Nachlin and Brett Singer make a Playlist for listening to at Work - .smil format for RealPlayer, as some players choke on m3u playlists; all freely downloadable music. I'm a little worried about bandwidth costs for the people whose songs get included in these playlists (mostly epitonic.com in this one), as there's no central caching and they don't get to display their adverts - Kazaa has shareable playlists too that automatically find and download each song when you play them, which might be a better way of going about it (as long as you only include free music).
See also My Mixtapes - playlists (though not automatic - could probably parse the pages for that somehow) for Emusic subscribers.
This post appears in channels: free_music