Directory of companies and business professionals

"Provides details of the organizational structures of these think tanks and research activities in which they engage, functioning as the 'soft infrastructure' for a global network of think tanks." Basic organizational information on ca. 500 institutions from 100 countires is available online.

Look at the Standard Directory of Advertising Agencies (the Red Book), a print source at the Lippincott Reference Desk. Also try an industry search (NAICS 541810) in the D&B Million Dollar Directory.