If you are looking for a U.S. company, you have many choices. If available an easy, free option is to check a print directory, such as the D&B Million Dollar Directory the Standard & Poor's Register, Gale Research's Ward's Private and Public Companies, etc. At least some of these are on the shelves of most mid-size and large public libraries.
Another option is to check out the subscription databases available through your organization or your public library web site. That may give you access to ReferenceUSA (highly recommended), the D&B Million Dollar Database (also excellent) and/or others.
Most businesses have phone numbers so, if you have some idea where the business is located, you can try any relevant telephone books you have on hand -- in print, on CD-ROM and/or the Internet. (For links to Internet phone books, see "Finding People" and/or "Telephone Numbers"). You could also call Directory Assistance.
In theory, companies doing business in any state are required to register with the respective state's Secretary of State, so if you know a state where the company does business, you should be able to look it up in that state's database of S. of S. filings. Most state have free online databases with reasonably good searching capabilities (For links to these Web sites, see "Secretary of State Records").
Some other suggestions: (a) Put the name of the company into Internet search engines (see "Search Engines") and search for a Web site with address information, (b) use Ci CorporateInformation to link you to good online sources, (c) if the company is likely to be public, search for an SEC filing (see the Filings section of "Securities and Exchange Commission") and/or (d) look for a Hoovers profile.
If that still doesn't do it, try the services you pay for, including Westlaw (BUS-TRACK), Lexis (FINDER;B-FIND), Accurint, KnowX, and/or Dialog's File 516 (Dun's Market Identifiers), File 518 (International Dun's Market Identifiers), File 521 (European Dun's Market Identifiers), or File 519 (Duns Financial Records Plus). Or you can call a business research service (I recommend NYPL Premium Services) and ask them to search their directories.
Other Options: Companies in the import/export business are listed in the PIERS Trade Profiles. You can search for and pull up the company profiles through Piers.com.
Corporate Affiliations: To find related companies, check The Directory of Corporate Affiliations (in paper, on Lexis (BUSREF;DCA), Westlaw (CORP-AF) or Dialog (File 513) or on the Web by subscription), get a Dun & Bradstreet Business Information Report, look for annual reports and 10-Ks (see the Filings section of "Securities and Exchange Commission"), search Dun & Bradstreet's World Base file on Lexis and/or search Dun & Bradstreet's Global Corporate Linkages database on Dialog (File 522).
Defunct Businesses: Locating companies that have gone out of business can be tough - defunct businesses are removed from most company directories and databases. One source dedicated to this purpose is Info USA's Inactive Business Database on Lexis (COMPNY;DBADCO), which provides the former address, phone number, a contact name and some minimal business information (e.g., gross sales, number of employees, SIC code). If the company had once been public, StockSearchIntl.com and/or OldCompany.com and/or the Directory of Obsolete Securities (Financial Information, Inc.) will tell you what happened to the company and, if possible, how to contact its successor. Other than that, try searching the relevant Secretary of State records, old print directories and old news sources.