According to the NY Times, Google will reveal tomorrow (Tues 6/24/08) a new AdPlanner tool that "was designed to help agencies identify sites where their target audience might be active. While it uses audience measurement data, AdPlanner also combines it with search engine data and information from third parties, to determine with more precision what sites attract a certain demographic audience. It then uses that data to help agencies determine where to place ads."

Read more at the Google AdPlanner