If you've got some fiber optics...

DIY Ring Flash!
One of the sucky things about most DIY ring flashes is that they're only set at one brightness. However, since this is mooching from the built-in flash, you're able to compensate and adjust the power of the flash. If anyone has a lot of time on their hands......
http://hackaday.com/2011/03/03/diy-ring-light-takes-its-cues-from-fiber-optic-toys/