Review New Startup - Trafficspaces (its like having a Facebook Ads for your site).
il: Heh, that's funny, I had the idea for this exact same product about a year ago, and never got around to building it. Props to you for actually executing.
Feature suggestion:
I'm more of an advertiser than a publisher, but as an advertiser, I would love the ability to search all sites registered with Trafficspaces, and bulk place ads on them. Similar to the AdWords content network. To appeal to advertisers, highlight popular/niche sites using the system. 
In order for you to succeed, you need monetary incentive for publishers to sign up, that is Trafficspaces will bring more revenue on a CPM basis than say, AdWords. To do that, you need to engage adveritsers to actively use the system.