There are many money making with advertising options available for android developers. There is the in-app model, such as Admob or Mobfox. Then there are the app wall options like those provided by AppBrain.
My favourite ad provider, Leadbolt has the most types of ad formats available. It is also the option for generating the most revenue! You should register now and start using Leadbolt in your apps!
This post shows how you can best optimise your Leadbolt notification ads and how to maximise your revenue and eCPM.