Google Gadget Ads have been tested over the summer and are now available to allow you to build and deploy multimedia widgets across the Google network and beyond. (This is a slow rollout to select advertisers for now)
This is a major innovation by Google that matches the power of desktop applications with the much needed solution of distribution. See the New York Times overview
The Webobedia has a new definition of the "Widgets." As a proud co-founder of this eternally helpful site, I am still amazed how quickly definitions need to be updated (this one is 10 days old and the Google Gadget Ads will be added soon)