Although there are tons of Ad networks in the Internet arena, however I will provide you a comprehensive list of the top 40 Ad networks to make money online from. These Ad networks are free to join but several of them have some terms and conditions which your blog needs to have.
1. Adbrite
2. AdDyamix
3. AdFish
4. Adknowledge
5. AdOn Network
6. AdSonar
7. Adsense
8. AdToll
9. Banner Connect
10. Bidvertiser Ads
11. BlogAds
12. BlueLithium
13. Chitika
14. Clicksor
15. CPA Empire
16. Crispads
17. Direct Media Exchange
18. ExpoActive
19. Federated Media
20. Gorilla Nation
21. Industry Brains
22. InterClick
23. JoeTev Ad Network
24. Kontera
25. LinkWorth
26. Mirago
27. Miva
28. Nixxie
29. OrangeFeed
30. Oridian
31. Oxado
32. Pheedo
33. RevenueScience
34. RevenuePilot
35. Rydium
36. TargetPoint
37. Text Link Ads
40. Vibrant Media