Elucify - A completely free software tool that uses crowdsourced data to find business email addresses
Clearbit - Clearbit provides Business Intelligence APIs
Lead Forensics - B2B website analytics and lead generation.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
FindThatLead Prospector - Feed your sales team with daily leads.
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.