Consumer.gov*Cool Site* - US federal government consumer information gateway. Find federal government resources on food, product safety, health, financial services, and other consumer topics.
Commodities Futures Trading Commission - Public information and complaints page, with information about enforcement activities, consumer alerts, reparations program, and other links.
Consumer Action Handbook - Published by the U.S. Federal Consumer Information Center. Includes help and assistance information for consumers including shopping advice, tips about products and services, and contact information for governmental agencies, business bureaus, consumer advocacy and protection offices.
FTC Bureau of Consumer Protection - Bureau of Consumer Protection's mandate is to protect consumers against unfair, deceptive, or fraudulent practices. The Bureau enforces a variety of consumer protection laws enacted by Congress, as well as trade regulation rules issued by the Commission.
Housing and Urban Development, File a Complaint - Consumer information and how to file a complaint housing discrimination, bad landlords in federal housing, violations of manufactured housing, land sale frauds, deceptive home improvement contractors, and other abuses and waste.
Office of the Comptroller of the Currency Customer Assistance - The OCC charters, regulates and examines approximately 2,600 national banks and 66 federal branches and agencies of foreign banks in the United States. Site has instructions on how to file a formal complaint.
Taxpayer Advocate Service (IRS) - Not exactly a complaint page, but does tell about help for problem situations in paying your taxes; from the Internal Revenue Service.