DiscoverOrg - DiscoverOrg is an IT sales intelligence platform providing technology marketers access to data, IT org charts, and real time projects.
Hunter - Find all the email addresses related to a domain
Clearbit - Clearbit provides Business Intelligence APIs
Apollo.io - Apollo’s predictive prospecting, sales engagement, and actionable analytics help the teams to reach its full revenue potential.
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Icypeas - This email finder has the capacity to bypass catch-alls