Founded in 1999 by the Center for Public Interest Research, Ecopledge works to "influence corporpate choices through a unique, multi-phased approach." Consumers, investors and students seek to negotiate with corporations and if that fails, they initiate a consumer, investor or employment boycott. Ecopledge has had a number of successes with companies in Responsible Shopper including Apple, BP and Whole Foods. Be sure to sign their pledge!
Campaign URL: www.ecopledge.com/about/index.htm