I stumbled upon the Friends of World Heritage website recently, and I liked their tips for responsible travel. They are focused on travel to visit the World Heritage Sites, but their recommendations are applicable to any kind of tourism or business travel. Much of the tips are fairly basic like "learn a few words of the local language," "don’t bargain aggressively," and "pack light." Much of it can be summed as, don’t be an ugly American.
The site provides a handy list of local tour operators to some of the Heritage Sites, so you can support a local business. And you can also book travel to one of the 851 World Heritage Sites via a partnership with Expedia. Proceeds from the purchase will go back to a fund supporting the protection and preservation of the Heritage sites, which sounds like a pretty good deal to me.
If you sign their "Responsible Travel Pledge" you get a cool set of desktop images of notable Heritage Sites, a screensaver, and a handy wallet-size travel tips.