Ring lights have a very specific light signature. Mostly it is connected with fashion photography as it gives out a very flattering light. The light is coming from around the lens, but since it is symmetrical it seems as if the light is coming right from the center of the lens.
Small strobe powered ring lights can be used for stills but if you want something really impressive, you would go with a huge wooden bulb-driven ring light. While those are a bit harder to transport, they give out a spectacular light that can also be used for video.
Check out the article here: http://www.diyphotography.net/how-to-build-a-kick-ass-4-feet-diy-ring-light/