Hunter - Find all the email addresses related to a domain
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.
Albacross - The world's first free B2B Lead Generation Network. Albacross help companies master their B2B digital marketing with Lead Generation and targeted marketing
Free Address Book - In our contact management software you can store fast and easily name, phone numbers, birthdays, address, company name, city, mobile numbers, insurance and loan info, e-mail addresses.
Upscribe - Embeddable lead generation forms for Medium
Clearbit - Clearbit provides Business Intelligence APIs