Google offers many AdSense ad units, but one that may not get as much attention as the others are ad links. Ad links were introduced in March 2005 and never really get too much credit from advertisers.
Ad links, also know as the link unit, can be in vertical or horizontal format. Here are two live ads that show some of the many formats:
A WebmasterWorld thread has several AdSense publishers praising these units. One said the ad link unit "has consistently yielded around 50% of my earnings." But senior member, Farmboy said, "my experience has been that a large portion of that 50% was cannibalization of ad units." Do they work well for you?
In my opinion, it all depends on the site, placement and the variables around it. So 50% for one person might be 0% for another person or web site. But clearly, if you haven't tried it, give it a try.
Forum discussion at WebmasterWorld.