From wired.com

The lack of good data on smaller websites has forced media buyers to rely on ad networks and giant web properties, but new site measurement firm Quantcast hopes to buck the trend.

Quantcast is offering site traffic and demographic data free of charge on over 20 million web properties, reports ClickZ. The firm does it by combining panel-based research with anonymous user info provided by advertisers, publishers and ISPs, and it's all available through a public, searchable database on Quantcast's site.

"The fact that these guys have visibility on millions of sites is very helpful as we're examining targeting opportunities and long tail opportunities," said David Smith, CEO of integrated media agency mediasmith, which has worked with the tool extensively.