The Security & Exchange Commission's database, EDGAR (Electronic Data Gathering, Analysis, and Retrieval), provides free access to 10-Ks, 10-Qs, proxies, prospectuses, and other documents.
"Short for Federal Reserve Economic Data, FRED is an online database consisting of hundreds of thousands of economic data time series from scores of national, international, public, and private sources. FRED, created and maintained by the Research Department at the Federal Reserve Bank of St. Louis..."
The Economic Census is the official five-year measure of businesses in the United States providing comprehensive statistics at the national, state, and local levels.