Clearbit - Clearbit provides Business Intelligence APIs
Leadfeeder - Leadfeeder converts your website visitors into sales. Connect your website's Google Analytics to Leadfeeder and unlock the power of seeing who`s visiting your site!
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
Visitor Queue - Better identify the companies that visited your website!
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Elucify - A completely free software tool that uses crowdsourced data to find business email addresses