Here's the scenario: all of our music is stored as mp3s. We want to be able to control music from a laptop as we sit in our kitchen or back room and have that music broadcast to speakers all over the house and back yard patio. Ideally we'd rather not have to run speaker wires from a central amplifier to the rest of the house. There seem to be 3 or four solutions to this problem.
Apple Airport Express and iTunes
Now that we're a family of Mac users, this seems like a decent solution. We buy a handful of Airport Express units ($100 new or as low as $60 used/refurbished) and install them in a power outlet near the speakers. The speakers have to have their own amplifier and accept a headphone mini-jack input for this to work. I'm also not 100% sure that the airports would all be synchronized in terms of what they play at the same time, though there are multiple articles which claim that it is possible. So, it probably works ;)
Bonus: Each of the airport express units expands the coverage of the WiFi network as well which will make our house super strong...and perhaps we could sell access to that to neighbors...
Drawbacks: iTunes only.
A Dedicated Device like Roku or Squeezebox
Roku and Squeezebox are two alternatives focused specifically on music. Roku is more focused on using the Roku to control the music, costs $200, and doesn't act as a WiFi repeater. The Squeezebox Receiver or Transporter could also do this but, like Roku, are way more expensive at $150 or $2,000 respectively and don't act as WiFi repeaters.
Drawbacks: Still requires some client software on the laptops that is Windows/Mac only :(