There are a few agencies.
Better Business Bureau has a small amount of clout, but is a membership agency; moreover, membership is not compulsory. There are other mmebership agencies that do similar things for its members, that are proprietary to certain functions: Automobile Association of America (AAA, or "Triple A") does things along the lines of hotels, mechanics, that sort of thing, that are held to certain standards (members join for roadside assistance benefits and discounts, among other things; businesses join for promotional reasons as a sort of franchise). Thing is, though, that's about all I know about. Other organizations exist such as EFF and ACLU, but those are more for protection of Internet rights and general civil rights, respectively, and are more concerned with government action.
In the governments, you have your attorney generals, your consumer protection bureaus, and then you have courts, be they small claim (typically less than US$5000, some variance), or courts that oversee larger judgement cases.
Overall, that's kind of how it works in the US. I wish we had a non-gov agency that did things like thi, though.
Hmm... how would one go about forming one?