I am looking into adserving services for a web application that is in development. I know there are the regulars like AdSense, DoubleClick, etc but the client wants the ability to sell of sections of the website to specific advertisers for specific campaigns. I would really prefer not to write this functionality (add, change, set duration, etc) from scratch so I'm looking for an adserving service that will allow specific ads to be uploaded and displayed to the end user. Preferably, one that integrates with a CDN of somesort.

Are there services that offer this functionality?