We are seeing more and more innovation in the ad space. A couple of interesting examples out there are:
AdBrite
AdBrite changes the game with connecting the buyer and seller of ad space. Instead of having to have a dedicated sales staff, a seller can signup with AdBrite and say "If someone offers me $x / wk/month/whatever to put an add HERE, take it".
Buyers can then browser around and find deals. "Ah, I want to advertise on that site, and $x seems fair". They broker the deal through AdBrite, ads get put on your site and you get paid. Everyone is a winner!