If you are a Gmail user and haven’t discovered it yet, here is a nifty little add-on which shows information about the person you are emailing or have received email from.
With the enhanced version of Rapportive, simply compose a message and enter an email address in the “to” field, as normal, and Rapportive will look up the contact and display a host of information on the individual in the right-hand side bar. If you include multiple recipients in a single email, Rapportive will look up each individual as you type their names.
On mail you have received, just opening the mail brings up the information about the sender, shows you recent communication between you and the sender and even allows you post comments to Facebook accounts etc.
You can get this nifty little add-on HERE. Must say it works very well while remaining unobtrusive in many ways.