Google introduced Custom Search Ads for AdSense today. These are AdSense ads designed for your site’s search results pages, so in effect, are similar to Google’s AdWords ads that appear in its own search results.

In hindsight, this offering seems like an obvious product for Google to offer, and will no doubt be a popular option for webmasters and publishers. If you have a significant amount of content, there’s a good chance your users may use your search feature.

Google suggests the ads for e-commerce, jobs, local, real estate, and travel sites. Google points to LemonFree.com and eCrater.com as examples of how some of its first publishers are using the ads. It looks Demand Media’s eHow is using them as well.

“In addition to great targeting, Custom Search Ads are designed to fit your existing search results’ look and feel,” says Google on the Inside AdSense blog. “Instead of pre-defined sizes, you can specify the precise width of each ad unit along with the number of individual ads to display, the ad layout, font size, font face, and much more.”

“With Custom Search Ads, we can rapidly develop and launch new search ad formats and extensions without requiring you to update your search code,” the company says. “For example, on Google’s results pages we’ve been busy testing new search ad extensions to provide users with information like locations, product images, page links, and merchant information. Two of these new formats are available today in Custom Search Ads: Ad Sitelinks and Seller Ratings. Ad Sitelinks extend the value of ads by showcasing up to 4 additional links to specific, relevant content within an advertiser’s site. Seller ratings add star ratings below a merchant’s ad aggregated from review sites across the web. These help highlight ads for merchants highly recommended by online shoppers. As new formats are developed in the future, we’ll continue to bring them to Custom Search Ads so you benefit automatically.”

Google says it is only accepting and supporting a limited number of publishers for now, but you can sign up here.