Arduino enthusiast and Instructables user "xenonjohn" has created a shield which contains the required sensors to build your own self-balancing device, and this has been demonstrated with his skateboard shown in the video below. The shield contains an inexpensive IMU unit, which is monitored via an Arduino that in turn controls the motor with the usual high-current motor driver.
Apart from a skateboard you can make your own balancing device using the generic shield design and your own motor controls and drive train. For more information and a very detailed explanation, head over to Instructables. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're new to Arduino and want to join the fun, the first step is a solid board for your projects - our Freetronics Eleven - the Arduino-Uno compatible with low-profile USB socket, onboard prototyping space and easy to view LEDs: