What devices can receive an AirTunes signal?

I'm trying to set up an in-home music system with built-in speakers. Right now I have my Apple TV plugged into the stereo outputting the AirTunes signal to the speakers. However, I'd like to get my Apple TV back at some point, so I've been looking into a replacement unit. The AirPort express and the Apple TV seem to be the only two devices that will seamlessly work with iTunes. New units cost $100, and even the used units command $50-$60 on eBay. It's also possible that I'd like to control several sets of speakers throughout the house, which would require several units for the different audio channels.

Are there any other pieces of hardware that will perform this task? What about software solutions? I'm aware of Rogue Amoeba's Airfoil, but this doesn't work well with the Remote app for the iPhone, and plus it requires that the software be installed and configured on the streaming computer. Are there any other solutions?

As far as I've been able to find, you've covered it:

• Apple TV
• AirPort Express
• Airfoil

I'm not positive, but I thought that you can use AirTunes from one Mac to another if they were on the same Airport Express network. I don't have my Airport Express hooked up right now. I'll have to test it out later.