Microsoft’s MSN Music beta offers RSS feeds. As Dave Winer points out, the Top 100 songs feed has enclosures with excerpts of the songs, which means you can play them by clicking the paperclip icon in FeedDemon’s newspaper.
It’s a shame, though, that these feeds have so many errors in them. Hopefully Microsoft will fix these problems, since their use of malformed dates means FeedDemon won’t show the publication date of each item.