FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
Email Verifier - Email verifier app lets you verify email.
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.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI