United States Citizenship & Immigration Services (USCIS)
United States Immigration & Customs Enforcement (ICE)
United States Customs & Border Protection (CBP)
United States Department of State (DOS), Visa Bulletin, Visa Wait Times, Find US Embassies.
United States Department of Labor (DOL), Online Wage Library, Legal Authorities, iCert Visa Portal System.
Excellent web resources:
American Immigration Lawyers Association (AILA)
Law Library of Congress
Immigrant Defense Project – Community Resources