Tap2Share is the best utility app you will find on the App Store. It allow you to share with one tap the screenshot you have just taken.
1º Take a screenshot holding Home + Power button
2º Swipe down to show the Notification Center
3º Tap the screenshot to share along with Twitter, Facebook, iMessage or any app you have installed
Easy right?
ProTip: You can even delete the shared screenshot if you dont need to do nothing more with it.