Raspberry PI - now with FM inbuilt!
So you looked down the Raspberry Pi spec sheet but weren't happy they didn't include an FM transmitter? No worries! I found it's possible to transmit FM using the clock generator built into the broadcom chipset. Just hook up a bit of wire as an antenna, and you're good to go.
Code and examples and a mini-explanation of how it works are to be found here:
http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter