I just ordered the Ermax undertail for the 08' S3. It shipped from Frog Specialties today. I should have it maybe Monday or Tuesday. I wanted the unpainted but they only had the Jet Black in stock.
I was in the process of making my own undertail but after all my careful marking and cutting I f'd it up. Oh well. The Ermax is the cleanest I've found and it was $209 shipped. Pricey yes, but I screwed the pooch with my stock fender. Will post pics once installed.
Here the pic from there site. Comes with the plate light and mount.