The Secretary of State's office in each state requires businesses to register. Local news media (newspapers, magazines, news outlets) are excellent sources of local business information. Academic business databases, public library business databases, business and industry organizations and associations are good sources of information for larger businesses. Publicly traded companies often have financial and other corporate information on their websites.
Find a Missouri business
Find information about a Columbia Missouri business
Find Information about Missouri businesses
OpenCorporates claims to be the largest database of companies in the world, gathering data from government and publicly available information.
Yahoo Finance an excellent source for company information.
United States Securities & Exchange Commission's Database of Public Company Filings
EDGAR (Securities & Exchange Commission's database of electronic public company filings)