V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
Clearbit - Clearbit provides Business Intelligence APIs
Adobe Audience Manager - Adobe Audience Manager is a data management platform that integrates online and offline data to deliver a unified view of all your audiences
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Google Audience Center - 3 votes and 6 comments so far on Reddit