When doing company research one should determine whether a company is publicly traded, privately held, or a subsidiary. Hoover's Online can aid you in determining this. If you are doing research on a local level where there are many small businesses, use a database like ReferenceUSA to make the determination.
Since it is difficult to find financials for U.S. private companies and subsidiaries, what you can do is to apply industry financial benchmarks. Use Bizminer (see below for link), a library subscription database, to do this. Before going there, first determine the industry NAICS code for your company by going to the Census NAICS search page located at www.census.gov/eos/www/naics. Enter the name of the industry in the search box, not the name of a company.
These sources will help you identify competitors. Hoovers Online and ReferenceUSA will also help you determine whether the competitor is public, private, or a subsidiary.
ReferenceUSA is a strong source for identifying competitors on a local level. Book of Lists is helpful for U.S. metropolitan areas like Denver, Colorado.