Google today has launched expandable ad units for those that have adsense enabled on their sites,and that have image ads enabled.This is only available to North American,and European sites that are in Dutch, English, French, German, Italian, Portuguese, or Spanish.
Will expandable ads alter my site's layout or be disruptive to my users?
No. In order to protect the publisher and user experience, we've created several policies around how expandable ads work:
Ads will expand only after a user clicks and interacts with the ad. Mouseovers or rollovers won't trigger the ad, in order to prevent accidental expansions.
An expandable ad won't expand more than double its width or height.
Once expanded, the ad will appear as a layer over the page content so that your content will not be modified or shifted in any way.
The user may close the expanded panel at any time.
All expandable ads must comply with our standard AdWords image ad policies.