Adbrite is a Pay per click network that offers banner ads, video units, and text link units. They also allow people to purchase ads through their marketplace on your banner units. I used them for a while and found them to be a poor earner. With that said, some have disagreed and have found them to be a great alternative to Adsense. I guess your mileage may vary depending on your site and site niche.

Signup for Adbrite