While I was already pretty well setup to accomodate (denon 3311 with optional zones 2 and 3 with preouts for zone 2) It cost me $100 bucks for an apple TV hooked up to my AVR, which has wireless control of which zones should be on/off via Iphone app, I simply have outdoor speakers on zone 2, main zone is the theater room, and zone 3 will soon be the main kitchen/den area. I have all external speakers from the theater running into a speaker switcher. There I can choose top outside deck, bottom outside deck, garage for zone 2 (This part is manual but what the heck, just do all this in a centrally located spot, you gotta run speaker wire anyways right?)
This all kind of depends on wether your speaker wires are all coming back to a centrally located amplifier or AVR, if so, the speakers switcher works wonders, if not, and you are using older avr's or amps in each one of the locations, the easiest option there would be to get a single AppleTV to run in the main listening/viewing area and then grab an airport express for each of the additional systems. Full control from your phone or ipod, as well as for your main area, a great option to use for youtube, missed tv episodes, and movies
I love walking in the door, pulling out my phone and hitting play on the apple remote app, there simply isnt an easier way to go about it IMO. With the new update you can now control the internal volume of itunes, and can stream directly from your phone as well so that is big plus. When friends come over and want to hear a song on THEIR device, they simply sign on to my wireless network and boom, they can control their whole playlist as well, it is GREAT! Now dont go off calling me a fanboy just yet, I pursued this avenue since I already have half the puzzle with an idevice and my whole library in Itunes, the only reason I suggest this way is since you mentioned it once or twice. If setup right, it beats any other option that ive found thus far... and for less if you already DO have most of the parts.
I didnt like how the sonus had a proprietary wireless setup and didnt integrate with what I already had going at the time.