AnyMailFinder.com - Find anyone's email address
Hunter - Find all the email addresses related to a domain
GitHub Email Finder - Find the email of any GitHub Developer using their GitHub username.
Norbert - Norbert is an online tool that helps you to find anyone’s corporate email address.
Paxtac - A free extension to find email with a full name and domain.
Mailmeteor - Send hundreds of personalized emails with Gmail.