V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
Clearbit - Clearbit provides Business Intelligence APIs
Lotame - Make your data actionable, learn about your most valuable customers, improve ROI by targeting the right audience and increase relevance across screens.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
Google Audience Center - 3 votes and 6 comments so far on Reddit
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.