Ads are a great way to monetize your application with providers like Google Admob
Having cloud storage enables new features like leaderboards and PvP. Providers include Parse.com and Google AppEngine
Don't fly blind after launch your app, analytics are crucial to the success of any game. Providers include Google Analytics
Find crashes before your users do, crash reporting is essential for building and improving applications. Providers include Crashlytics and ACRA
Let your users show off their high score on Facebook, or allow players to create a persistent profile. Providers include Facebook SDK and Parse.com
Unify billing across all platforms, Providers include Google Billing, Amazon Billing