Fresh off the completion of their Doubleclick deal, Google has released Ad Manager. The system is designed to help publishers manage ad placement, pick the highest-performing ads and fill unsold inventory - essentially offering an ad exchange network free of charge. The site is completely hosted on Google's servers. Here's how it works:

Publishers place the Ad Manager code on their sites, which then tracks page views and click-throughs to provide statistics on each ad unit. Ads tracked can include graphical, text and video. Ads can even be geo-targeted by examining the visitor's IP address. The service supports other ad networks as well. It's free to use, but Google will get a piece of the action by providing AdSense ads when a unit goes unsold or remnant space is available.