The Online Publishers A ssociation have partnered with some publishers to try out new ad units. The standard:
The Fixed Panel (recommended dimension is 336 wide x 860 tall), which looks naturally embedded into the page layout and scrolls to the top and bottom of the page as a user scrolls.
The XXL Box (recommended dimension is 468 wide x 648 tall), which has page-turn functionality with video capability.
The Pushdown (recommended dimension is 970 wide x 418 tall), which opens to display the advertisement and then rolls up to the top of the page.
Here is a screenshot of what looks like a new version at the New York Times.