Clearbit - Clearbit provides Business Intelligence APIs
Hunter - Find all the email addresses related to a domain
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
Albacross - The world's first free B2B Lead Generation Network. Albacross help companies master their B2B digital marketing with Lead Generation and targeted marketing
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Upscribe - Embeddable lead generation forms for Medium