CPM stands for Cost Per Mille or Cost Per Thousand Impressions. Most ad networks pay anything upwards from $0.50 to $5 and higher which depends on the ad network. Basically, you earn that amount every time your blog receives thousand impressions.
Here is a list of 10 best CPM networks:
1. Google Adsense
2. Tribal Fusion
3. Casale Media
4. Advertising.com
5. Value Click
6. Adpepper
7. Burst Media
8. Adtegrity
9. Vibrant Media
10. Gorilla Nation
If you aren't happy with Cost-Per-Click(CPC) then you should definitely try one of these CPM networks for better results.