Rapportive (link) is a free Firefox, Safari and Chrome add-on that brings social intelligence to GMAIL. For every email sender, it displays a picture, a brief bio,  location and links to that their social networks. 

Yes it does work with Google Apps accounts.

It replaces the (less useful) GMAIL advertisements with its own information. Another company called Xobni has a similar tool for Outlook. Installation took only a couple of minutes and then it automatically performs its magic anytime you use the GMAIL web interface. 

There is some debate about where the service get's it's information from. Some have claimed it comes from a service called Rapleaf, others claim it is an in-house culling service. All we know is that the company provides this blurb:

"We combine information from several sources; at the moment, these are Academia.edu, AngelList, Bitbucket, CrunchBase, Econsultancy, Facebook, Flickr, GitHub, Google Profiles, Gravatar, LinkedIn, Plancast, Posterous, Stack Overflow, Tungle.me, Twitter and Vimeo, as well as thousands of organisations' public websites. " (link)

In my testing, some contacts come jam packed with useful information and others get wrong or missing info. Overall I think this is a great way to gleam additional  information which can make the difference between winning or losing. 

Give it a try. It's free