Apple never ceases to amaze: AirPort Express and AirTunes. Nuts.
For US$129 you can’t go wrong. Can’t wait to get my hands on one of these things. Not only does it allow you remotely control what’s playing from your main computer but it is also a fully-fledged base-station. It can also be used in an existing wireless network to extend the range to your current base-station. Love your work, Apple.