Adbrite?

ADBRITE
AdBrite, "The Internet's Ad Marketplace", is an e-commerce site
Like Ebay, many AdBrite users are both buyers and sellers (advertisers and publishers). That's why our homepage doesn't say "advertisers go here" and "publishers go there". There are, however, two distinct things you can do with AdBrite -- buy and sell ad space -- so we'll address them separately here.
If you're an advertiser, AdBrite provides great deals from all sorts of websites. Search or browse to find a site you want to advertise on. We'll show you relevant stats, including price and how many clicks you can expect. Add it to your cart, write your ad, and pay. If approved by the webmaster, your ad will appear on that site at the scheduled time.

If you're a publisher, use AdBrite to set your own ad rates, and approve or reject every ad that's purchased for your site. AdBriteenables you to instantly sell ads to your visitors via a "Your Ad Here" link, in addition to selling through AdBrite 's marketplace and sales team.