NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Clearbit Connect - Clearbit Connect is a free extension that surfaces actionable information on the people who email you.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.