While Yahoo and Microsoft continue to struggle to gain ground on Google in online advertising, Google continues to advance.
Google has announced that they are now accepting third-party ads on the Google content network. This should be helpful to AdSense publishers because it will offer an even larger variety of advertising in the content network and it will increase the inventory of display ads. Google believes this will increase the revenue for a lot of AdSense publishers.
Many big name AdWord advertisers who use third-parties have been wanting Google to do this for a long time.
Details from Google:
Inside AdSense: Introducing third-party ads on the Google content network