Google AdSense provides CPM based ads in addition to the normal CPC ads.
Here are some more that allow smaller publishers:
Once your reach 500K+ impressions, do give TribalFusion a shot. They have higher requirements, but do have some of the highest CPMs.
Adtomatik is also an ad network. I've been using it for a year and the result couldn't be better. The best service. I totally recommend it. It's brand safe and my revenue has totally increased since I started using it. Definitely the best I've ever discovered.