Take a look at the Nikon R1C1 outfit, whilst it's not a ring flash when used with the supplied extreme close up adaptor it performs as one. You have the added benefit that the SB R200 flash units can be used wirelessly as fill in flashes if you have other speedlights and the accessories supplied with the kit are quite extensive. If your D80's own flash can be used as a commander (I believe it can) then you can get the R1 kit (which is the same but without the SU800 commander unit) for just a few quid more than the Sigma ring flash. Highly recommended!
Hope this helps, Andrew
PS. I also have a ring flash but it's very seldom used now.
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