D&B Hoovers: Extensive access to public and private company profiles and regularly updated industry profiles. You can also find information about a particular company's main competitors, and SEC filings for public companies.
Mergent Online: provides access to current and historical financial information on 15,000 U.S. and 20,000 foreign companies, both active and inactive. Included are firm descriptions, statistics, financial information, and annual reports. Mergers, acquisitions, joint ventures, long-term debt, bond ratings, capital stock, insider trading, etc. are provided in the company records.