US Department of State - Bulgaria
Country portal offers a map and links to Background Notes, Country Study, the US embassy and the current ambassador, press releases, fact sheets, annual Human Rights Reports and other major reports including Industry Market Reports.
http://www.state.gov/p/eur/ci/bu/

CIA - The World Factbook: Bulgaria
Features map and brief descriptions of the geography, people, government, economy, communications, transportation, military and transnational issues.
https://www.cia.gov/cia/publications/factbook/geos/bu.html

US Library of Congress - Portals to the World: Bulgaria
Annotated directory of selected online resources.
http://www.loc.gov/rr/international/european/bulgaria/bg.html

NationMaster - Bulgaria
Profile includes information for various aspects of the country, with a special emphasis on statistics and rankings.
http://www.nationmaster.com/country/bu-bulgaria

Wikipedia - Bulgaria
Hyperlinked encyclopedia article covers the country's history, government and politics, geography, economy, demographics, language and culture.
http://en.wikipedia.org/wiki/Bulgaria