New ad network that works alongside admob
http://www.leadboltapps.com/appwall/
I've been using it for a few days and its definitely worth trying out. Just sign up, add the link they give you and when your users click it takes them to a list of free apps. if they download one u get paid. Monthly by paypal. Developers can sign up free here http://www.leadboltapps.com/web/publishers/signup.php?ref=10035849