American Association of Advertising Agencies.
Links to related advertising organizations and government sites and news releases.

The Advertising Red Books: Agencies.  
Information Desk 1 HF5805 .S781
Covers essential facts about advertising agencies including clients, billings and personnel

The Advertising Red Books: Advertisers. 
Information Desk 1 HF5805 .S7
Provides financial overview of companies spending at least $200,000 on national or regional advertising campaigns - gives listing of kinds of media used (ex. billboard, cable etc.)

American Advertising Federation
Links to industry associations and publications