Sonos is great, and Logitch Squeezeboxes are a lower cost (but more setup required, but more customizable)
You could also look at getting a second receiver and connect it to your computer. If you get one that supports it, you can use an android/iPhone app to control it remotely. If you don't care about playing different sources in different areas, a cheap speaker selector would work. Will probably be cheaper than Sonos.