Rapportive is a plugin for using with Gmail — it adds a small panel to the right when you open any email, with information about the sender. It consequently also looks the sender up on various social networking sites, such as Facebook and LinkedIn.
As of today, it even looks on Bitbucket! Observe:
I (Jesper) have been using Rapportive for quite a while, and take it for granted that information about the sender will appear next to the message body. Would hate to be without it.
You can read more about Rapportive here.
