I'm in the same boat - Sonos plus the old freebie Spotify. The nearest you can get for free (unless anyone here knows better...) is the Blinkbox "radio" that comes installed with the app.
I used to like Last FM, but that closed down :(
I'm very happy with the Sonos, though, and planning to get a Connect so I can use it with my existing hi-fi amp and speakers in another room.