The Raspberry Pi can be used for a number of applications from a media centre to a light painter. The latter can achieve some incredible results as can be seen below:
Although I wont go in to full details here, they can be found over here, I will quickly mention that this project ran a little smoother than expected. The RPi is used with an install of Occidentalis as the regular Wheezy install isn’t quick enough with outputs to handle the data required. 3 pins are used which transmit to the RGB LEDs which are backed by a PSU as the RPi doesn’t output enough power.
The contraption is put together on a bike (for the picture below) and gave the following results. Other items had LEDs attached to achieve other results.