Google also announced a new 300x600 AdSense ad unit, "is one of the fastest growing sizes by impressions," google mentioned in the recently released Display Business Trends.
"300x600 sometimes referred to as a half page unit, provides a larger space for advertisers to get their message across and can offer users rich engagement," google stated.
Because "this unit is new to our network, you'll currently see a large number of text ads in these placements. Over time we'll continue to build a wide range of text and display ad inventory eligible to appear in this full slot as well," Google added.
Google notes, as with all ad sizes, "it's important to carefully consider the placement of ad units to ensure both users and advertisers have a great experience with your site."
For more information on the performance of potential placements, check out the heat map in the AdSense Help Center.