Mergent Online Easy access to 15 years of balance sheet, income statements and cash flows.
ValueLine Access to ratios, financial benchmarks and quotes.
Morningstar It's not just mutual funds, 10 years worth of financial statements, ratios and analyst research.
YahooFinance Free access to stock prices, financials, ratios, news.
SEC 10K (Securities & Exchange Commission) 10K is the name of the file U.S. companies that raise capital on the public markets are required to file annually with disclosures about their operations and financial condition. Authoritative and detailed. EDGAR is the governement site for all filings
Datamonitor Basic company description, facts with strenghs/weaknesses/opportunities/threats analysis. Public and private, U.S, and foreign companies.
Hoovers Company Records Best known for pithy descriptions. Public and private companies, U.S. and foreign companies
Lexis-Nexis Academic Aggregator of company data from a variety of sources including Sungard, Hoovers, Disclosure, Directory of Corporate Affiliations and Standard & Poors. Links to news articles, intellectual property filing and legal cases.
ReferenceUSA Business directory including small private firms and publically traded international companies in the OneSource module.
ABI Inform A good basic business article database. Content balanced between trade news and academic research.
Business Source Premier Another good basic business article database. Best source for scholarly articles.