Google AdSense has announced that they now accept display ads from third-party vendors.

“Third-party ad serving will introduce a greater variety of advertising into the Google content network, increase the inventory of quality display ads competing to show on AdSense publisher sites, and offer more engaging ads for end users.

In the long run, we believe the increased inventory and ad competition will result in increased revenue for many AdSense publishers.”

In order to allow third-party ads on your site, you’ll need to do the following in your AdSense account:

• Opt into image ads
• Enable advertisers to target your AdSense channels
• Opt into placement targeting

More details at http://adsense.blogspot.com/2008/05/introducing-third-party-ads-on-google.html.