Hunter - Find all the email addresses related to a domain
Cardhop - The Mac contacts app you'll want to use.
AnyMailFinder.com - Find anyone's email address
Webby - Webby allows to use Facebook, Youtube or any web app as a regular desktop apps, integrated with the...
Norbert - Norbert is an online tool that helps you to find anyone’s corporate email address.
NetHunt CRM - Turn Gmail into a smart CRM