Chrome: Got a mail from someone you don't know? One easy way to look up information about them is to get Vibe and just hover your cursor over the email address.
Vibe is a lot like Rapportive, but with a few differences. First, it isn't restricted to the inbox alone, it'll work across your browser anywhere that an email address is noted. Second, it's not limited to a single email address in a message. Once you have the app installed, hovering your cursor or highlighting an email address will have Vibe issue a drop-down pane from the toolbar with all the details you need about that person: profiles on different networks (LinkedIn, Facebook, Twitter, Google+, and even a web page they are most likely to be associated with), a short description, and keywords that best describe that person.
In most cases, the information it showed me was accurate but Vibe isn't smart enough to cross-reference a person's work and personal accounts. Still, it gets the job done for showing you a quick information pane about most people.
Vibe (Free) | Chrome Web Store