Google AdSense well known for the traditional text and graphical advertising is planning to move to rich media, including interstitials, expanding ads and floating ads.
Jensense reports about these new types of ads
“Floating ads are ads that either stay on top as the page is scrolled, or ones that “float in” from the side of the page to the center of the page. Expanding ads are those that require user interaction to expand, either with a mouseover or a click. Interstitials are perhaps the most interesting addition to this rich media beta, because they are a format that people love to hate, and that are often more annoying than pop-ups. You have likely stumbled across an interstitial ad – they appear when you click through to read a page, and before they will show you the page, you are bypassed through to a full page ad that you must view before seeing the actual content you were wanting, often by having to click a link on the interstitial ad page.”
They further inform that this is an invite-only beta test to which only a small number of publishers were invited to.