Cool tutorial on how to Build your own Ring flash (via strobist).
From what i see you basically you mount a flash pointing into a cereal box which has had the insides covered in tinfoil, and direct the light out in a circle cut in the cardboard that your lens is poking through. Pics and instructions on the page provide a better view of it though, but it did take me a few minutes to grok what the heck it was doing 🙂