We are using these this year, fits the camera well and are quite bright:
http://www.ebay.com/itm/181239714879... 4.m1439.l2649
They ship out of china, so I wouldn't suggest buying them from this particular seller. A 60mm light ring shipped out of the US should do the trick. Any color will work, we have used blue in the past with success. Green is a good choice though because there aren't many light sources or field elements that are green. Also we usually run these at around 9v instead of the intended 12v just to bring the brightness down to a non-obnoxious level.
We then calibrate the camera so that it returns a completely black image, except for the target, which is the color of our light ring. I believe we adjust the white balance, exposure, and contrast levels to achieve this. Calibrating the camera properly will make detecting goals quite a bit easier in software. I believe there is a white paper on calibrating the camera this way, but I am unable to find a link at this time.