MobFox is known for being a well-paying ad provider for the European and US market. The good thing is that they natively support a backfill option. At the moment, this is InMobi. Backfilling means that whenever MobFox can't provide an ad, they will use your backfill settings to show an ad from your backfill provider. InMobi is very strong in the Asian market, and so many countries and continents are covered through MobFox/InMobi.
The MobFox website is located at http://www.mobfox.com/.
Just sign up for a publisher account there and enter your personal and payment details. After this, you are ready to implement ads into your game.
To be able to display ads in ...