ICRS) is a student-led university club aiming to increase robotics interest at Imperial College London and across the UK.
They run workshops, competitions and lectures to teach about robotics, electronics and software as well as providing help (financial and technical) to students looking to start a robotics project.
They also run several robotics beginners courses and have also recently won the highly prestigious John Lever Memorial Award for their outstanding courses and robotics talks.
One of their latest projects was to use a Raspberry Pi as a low powered radio transmitter.
Their design required absolutly no specilaist hardware, just a short aerial connetec to one of teh GPIO pins and the signal was detectable up to 50m away. Their tests were with audio signals, but I can't see why they couldn't also be used to transmit digital data, although you almost certainly would need a proper circiit to dtect it on a Pi.
In The UK you need a license to tranmit on certain frequencies, and as this is right next to Radio 2 I would think this might be dodgy ground, so best check before trying it for yourslef.
(Found via Make Blog http://blog.makezine.com/2012/12/10/raspberry-pi-as-an-fm-transmitter/?parent=RaspberryPi)