"[F]ree online community of nearly 50,000 experts, media and professional communicators. Profiles are searchable by keyword and geographic location, and include photos, video, links to white papers and more. You can also create your own profile on the site to showcase your own expertise; view leads on experts and story ideas; participate in forums; and more." Requires registration for free account.
Directory information for US private and public companies with rankings by sales within SIC and NAICS codes and state rankings.
More InfoVolume 4 has a Geographic Listing by State/Zip Code and then they designate the status of the company R=Private P=Public. (San Diego County Library (SDCL) has information from this book in their database Business and Company Resource Center).