EDGAR - SEC Search
All public companies are required to file financial data such as the 10-K (annual report) and 10-Q (quarterly report) with the U.S. Securities and Exchange Commission. Not all documents filed with the SEC will be available on EDGAR. You can also try LexisNexis - they have full-text filings from 1993 forward and selected filings back to 1985 (click SEC filings under Companies in the left hand navigation bar).