NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
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
Drupe - Next generation contact manager and dialer.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Simple Contacts - Contact lens prescriptions from home