I like the look of Amazon's native shopping ad from their Associate program. It relies on page content and the to serve related ads, but like Adsense. I installed it yesterday on two of my sites and on one of them the ad is showing only one page so far and on the second it's not showing up at all. Both sites perfectly satisfy their terms and conditions. And most of the pages on both sites are closely related, meaning if the ad shows up one page then there is no reason why the tool shouldn't be able to generate ads for othe pages.