American Marketing Association
http://www.ama.org/

Advertising World
http://advertising.utexas.edu/world/
"Resources for advertising & marketing professionals, students, and teachers. The most extensive collection of advertising-related links on the Web!"

Adage.com Advertising Age
http://www.adage.com
From the Ad Age Group, publishers of Adverstising Age

CI Strategies & Tools I3 Internet Intelligence Index
http://www.fuld.com/i3/index.html

Marketing Virtual Library : Knowthis.com
http://www.knowthis.com/

Ad*Access
http://scriptorium.lib.duke.edu/adaccess/
"...presents images and database information for over 7,000 advertisements printed in U.S. and Canadian newspapers and magazines between 1911 and 1955."

Adflip.com
http://www.adflip.com
"...world's largest searchable database of classic print ads."