Here are some governmental websites that provide useful information about U.S. immigration laws and other related services:
www.uscis.gov (U.S. Citizenship and Immigration Services)
www.travel.state.gov (U.S. Bureau of Consular Affairs)
www.ice.gov (U.S. Immigration and Customs Enforcement)
www.dhs.gov (U.S. Department of Homeland Security)
www.usembassy.gov (Websites of U.S. Embassies worldwide)