"There's a disconnect between Silicon Valley and Madison Avenue," says Konrad Feldman, CEO of leading Web media broker Quantcast, "and we're filling it." The company, which sets the standard for audience measurement, sifts through its mountain of data—more than 200 billion observations of media consumption every month, a Web visibility second only to Google—to answer both the what and the who behind the numbers. Quantcast can discern who's clicking on ads, visiting a site, and buying the products, and then find clones of that audience across the U.S. Web population. "We define the look-alike and then let you buy the look-alike," Feldman says. Its newest program, launched in June, has already attracted the likes of ABC, CBS, MTV Networks, and all of the top 10 media-buying agencies in the United States. Quantcast is now working with TiVo to marry TV and Web data, letting marketers see not only how their TV ads are performing but also which shows and ads its Web audience likes.