Contextual-ad services are the hot new thing among small and independent Web sites. Even small Web sites with no advertising sales force can generate noticeable revenue from the ads placed on their sites. Contextual-ad services provide Web sites with text link ads that are relevant to the site's content. Some of the services even give the Web site owner the ability to block competitors' ads or offensive ads. Contextual-ads generate more money because the ad services use search engine technology to make sure the ads relate to the content of the particular page on which the ads are served. In turn, that increases the number of click-throughs. The more click-throughs, the more revenue the site earns.These services are far more lucrative than link exchanges or affiliate networks, which have been around for years. Contextual ads are helping Web site owners monetize their sites. Some Web site owners are finding that what was once a labor of love now generates enough revenue to pay for overhead and sometimes even a part-time salary.Who are these contextual-ad services? Google's AdSense is the largest, followed by Overture Content Match, About's Content Sprinks, and Espotting Media's Content Monetisation. Google's service is already acknowledged to be the best. And, now that Google has announced it will be acquiring Content Sprinks, Google is shaping up to become the overwhelming leader in this space.