i have a Sunpak DX-12R ringlight that has worked very well with both 2 1/4 and 35mm. Another approach which may suit your needs and would be less costly as well as not producing the donuts when photographing something that is reflective would be to get a macro flash bracket from Bogen and use two small flash units (which you may already have?) and set them at 45 degree angles. That would give shadowless light or for other effects one could be set at a different output, etc. That way you would not be tied to the ringlight when other situations needing a flash present. I have one of those and use it with a couple of small Vivitar flash units.

http://www.jeffreyglasser.com/