Online Searchable directory of over 100,000 public and private companies with links to their web sites. CorpTech Directory of 45,000 high tech manufacturing and development companies.
Detailed profiles cost money.
Hoovers Short profiles of over 12,000 public and private companies. Pay services provide more detail. Edgar Database of Corporate Information Information from the US Security and Exchange Commission includes extensive financial information on publicly owned US companies. Thomas Register Directory of 155,000 American manufacturing firms. Search by product, service, company names and brand names.