La Mode Ethique is an international guide of ethical fashion brands and designers. The website, which is still in development, lists a good choice of labels. Of all the listings so far, this is until now the best one. A shame of all the google ads around, and also the flash thing is a bit unfunctional, but it is a great source and also professionals can still find a lot of new, cool designers here.
I also just wrote about Bransparent, another promising listing of ethical brands, who do a sustainability check up with every brand they ad to their list.
Still all these listings are far from complete. We created a much longer list of labels as any list we found on the internet so far. Maybe we should sell it over e-bay ;)