Hunter - Find all the email addresses related to a domain
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
Apollo.io - Apollo’s predictive prospecting, sales engagement, and actionable analytics help the teams to reach its full revenue potential.
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
Icypeas - This email finder has the capacity to bypass catch-alls
Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.