Hoover's: US business directory; only some of the information is available for free
SEC Filings & Forms (EDGAR): from U.S. Securities and Exchange Commission (SEC); submissions by companies and others who are required by law to file forms with the U.S. Securities and Exchange Commission (SEC).
Strategis: from Industry Canada; wide range of company of industry information; geared towards exporters
Thomas Register: a US directory of manufacturing goods and companies
