The freely available version of Hoover's (a D & B company) has information on larger public and private companies. For public companies, this generally includes sales, income, officers, officer bios and salaries, directors, and company description. There is less information available on privately held firms and smaller firms. Research has access to a more inclusive version of Hoover's, which ties into D&B's extensive database. In most cases, though, the level of detail on very small firms is limited to estimated sales and number employees.
Lexis-Nexis Academic (available from computers on campus, or off-campus if authenticated through a campus server; otherwise this source may be available at your local public library):
The default page for Quick News Search features a box at the bottom right for Company search. You can select US public, US private or international company reports. Sources include Hoovers, US Business Directory, Standard & Poor's, etc. This is a very powerful search and pretty much the same as the full- strength version that the research department uses.
Other company databases can be found through the Jackson Library page at Stanford's Graduate School of Business. Off-campus Stanford users can access some of the databases and news sources by using EZProxy.