Google AdSense Section Targeting plugin will help the ads being displayed be more releveant to the content on your pages.
Section targeting allows you to suggest sections of your text and HTML content that you’d like us to emphasize or downplay when matching ads to your site’s content. By providing us with your suggestions, you can assist us in improving your ad targeting. We recommend that only those familiar with HTML attempt to implement section targeting.
This plugin lets you determine the areas of your site that will be used to select ads.
Google Section Targeting : https://www.google.com/adsense/support/bin/answer.py?hl=en&answer=23168