You know an AppleTV with an iPod Touch does almost all the things you listed and still comes in cheaper than Sonos. iPT is a great remote control for the aTV (and of course does a million other things too). aTV can do internet radio -- I use that all the time. You make a playlist in your iTunes of radio stations that you like and then sync the playlist to the aTV. You don't need the iTunes computer on to use the radio stations once you've synced. A poorly advertised but excellent feature of the aTV.
Lastly, you can do multiroom music for parties by adding airport expresses (also cheaper than Sonos). The aTV can be the source (no computer needed if you've synced your music to the aTV) and each aTV/airport express can be individually turned on/off and volume controlled by the iPT. Oh, and if you want to skip a receiver just hook up the express to powered speakers (like Audioengine speakers) or even better to a unit with wireless speakers (like Griffin Evolve) and then you have portable speakers, controlled via the iPT, that you can bring to any room or outside for parties without any wiring.