I stumbled over this today
http://www.loc.gov/rr/business/company/private.html
Which is a guide to private company research available at the Library of Congress.
The Library of Congress also has a guide to public company research and international company research. These guides are designed to give someone searching for company information some ideas and strategies for finding this type of information.
The Library of Congress also provides other business services, including a great list of internet resources here:
http://www.loc.gov/rr/business/beonline/subjectlist.php
Enjoy our tax dollars at work.