Ripenn has completed a study analyzing 3,016 headlines from 24 top content sites. Some nice little cheat sheets in there as well.

Your Perfect Recipe for Headline Writing via @Buffer

So many different variables go into a viral post—timing, emotion, engagement, and so many others that you cannot control. There is no viral blueprint. The greatest chance we have to understand viral content is to study the posts and places that do it best, figure out what worked for them, and try it for ourselves.