RocketFM - FM Transmitter for Desktop Computers

Griffin Technology: "RocketFM uses any available FM frequency to transmit audio through your home, car or office stereo system. Applications such as iTunes, GarageBand, video soundtracks and even streaming internet radio can be conveniently broadcast with RocketFM."

I'm a fan and a user of Griffin's iTrip, these might be a neat (and cheaper) altertative to Apple's Airport Express + Airtunes. It promises a 30ft range.