I have been using some of these resources for a long time, but never thought to put the links here :doh:
http://www.isafetrade.com/ - a very useful addition to the scam-fighting scene. Has a large database of known scamming, fraudulent companies and good reviews of trustworthy safe internet and international traders. Free for a lot of stuff. You can sign up to get a login account for more detailed information.
http://www.manta.com/ - searchable database of virtually every registered company in the developed world, and quite a lot of other places as well. If you register you get a regular "Business Advice" newsletter and regular updates on global trade.