If you're worried about parking your car in a small garage, or have problems judging distances - this project by Instructables user "rclymer" will be of great help. Using an ultrasonic distance sensor, it feeds the vehicle's position relative to the wall to an Arduino (or ATiny) which then articulates the data using an RGB LED. You can program in the required distance and then when you're close the LED will change colour.
There's a lot of scope to modify this project, including adding audible warnings or ever a few more LEDs for visual indicator of distance. Either way, check out the project page for more information. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
If you're looking to make more creative designs with LEDs, consider the Freetronics RGBLED: full colour module. It includes a bright RGB LED on the top of the board and a WS2801 constant-current, addressable, multi-channel LED driver on the back. This smart module can be daisy-chained, so you can connect a number of these together in a string and drive each of the module colours individually from your microcontroller. For more information and to order, visit the product page.