Common Sources of company information include:
Most companies will post their current and some previous annual reports on their corporate websites. AnnualReports.com provides the most recent annual report for most corporations in pdf and html versions.
Required company filings with the U.S. Securities & Exchange Commission (SEC) may be viewied online in its EDGAR service.
The following sites can provide additional information on companies such as major holders of stock or a listing of manufacturers (ThomasNet).
This tutorial from Chad Boeninger from Ohio University demonstrates how to create a company comparison report using Mergent Online.
This tutorial from Ohio University demonstrates how to use S&P Net Advantage to compare companies.