Smartr Inbox for Gmail is a sweet little Google Chrome extension which enables you to keep up with all your contacts, right in your Gmail. It will connect your friends and contacts emails with their Twitter and Facebook accounts. It will gather as much available information about your contacts and blend them all together, so you have details from a mobile number to a picture of them. It builds complete profiles on as many contacts as it can. You can even check your message history, for example since when you first got in contact with them and even how many emails you have exchanged. It's practically a huge address book.
You can also keep this all in sync between your phones but unfortunately there is an annual/monthly fee. Hey, these guys got to make money right?