I've been working on using Airfoil to do whole-house voice notification on system events; the door locking, the A/C getting changed, etc. Airplay seemed like the easiest way to accomplish that.
I dug around and found this speaker, the iHome iW1 on Amazon; I figured it would be an okay starting point: cheap, but not completely terrible.
It turned out to be a pretty decent-sounding speaker, especially at a $50 price point. It's definitely cheaper than my original solution of using Airport Expresses and plug-in speakers in every area (though, I do have one extending solid wifi coverage upstairs). Setup was pretty easy; just install an app on your device and connect to its wifi directly. I've had no problem with it holding settings, even after it discharged for a couple of days.
Once I outfit every area (two bedrooms upstairs, and the kitchen/dining area downstairs; I have the initial one in my office), I want to look at using motion detection to decide which rooms should receive the audio.