Consult the U.S. Bilateral Relations Fact Sheets (formerly Background Notes) for your country from the U.S. State Department.
Look for the appropriate Country Commercial Guide compiled by U.S. Federal Government agencies.
Some of the other U.S. Government sources are:
General information on countries of the world are also available from other governments and intergovernmental sources, as well as from multinational firms offering business services:
International and Intergovernmental Organizations