A little known fact is that while Google places strict limitations on how you shouldn’t draw attention towards AdSense ad units, they encourage you to actively endorse the downloading and usage of products you refer through Google Referrals.
You earn a lot better (upto $1) than clicks on your average AdSense ads, if you can gain a convert – i.e. get a new user to start using any of the listed products (AdWords, AdSense, Firefox with Google Toolbar and Picassa) for the first time. To increase your chances of getting a visitor to click the referral link, Google tells you to devote a write-up on the usefulness of the product and then draw a visitor’s attention to the referral button. To the left is an example provided by Google.
Moreover, instead of placing the referral link in the spots where you place your standard ads, try and include them somewhere in the actual content of your site, thus enabling the visitors to follow your preachings 😀 and arrive directly at the link in one smooth flow.
They even advise you to keep rotating the referrals and try and make them relevant to your content in order to further increase the chances of a click.
Incidentally, if you’re using WordPress 2.x and are interested in placing a such referral unit in the sidebar of a widget enabled theme, I’ve created a drag-and-droppable widget called GARR (Google AdSense Referral Rotator), which will keep rotating between the available referrals on every page load. You can see it in action on the right-most sidebar on my home page.
A whole set of such advices and trips & tricks on AdSense Referrals (compiled by Google) can be found here.