Google AdSense is an advertising program for webmasters that truly represents breakthrough stuff. For example, say you have a site on the history of Indiana Basketball. If you placed an AdSense banner on your site, it would generate contextually correct advertisements: autographed Isiah Thomas posters, Bobby Knight memorabilia, etc. It's a two-fold win for advertisers and publishers: the former get their targeted audience automatically (without having to pick among thousands of placement options) while the publishers get higher revenue because of superior clickthrough. As an aside, BadBlue's free version is currently generating around 300,000 AdSense impressions a month.