Apple has rolled out its iAd programme to developers, which means they can buy ads to promote their own content in other apps. Apple will be charging developers 25 cents per iAd click, which is a significant discounts from what it charges brand advertisers ($2 per click, 1 cent per impression).
The good thing about iAds is that user can download advertised apps from the App Store without leaving the app they're in. Once they are done looking at the advertisement, user will be taken back to the app. Its really an ad within an app!
The iAd Network allows developers to exclude ads from competitors or other unwanted advertisers based on specific keywords, URLs, and application Apple IDs. This will definitely open up more opportunities to many developers to market the new apps.