Crunchbase - Crunchbase is a platform for discovering industry trends, investments, and news about companies around the world.
DiscoverOrg - DiscoverOrg is an IT sales intelligence platform providing technology marketers access to data, IT org charts, and real time projects.
CB Insights - CB Insights is a company database for the venture capital and corporate development community.
Clearbit - Clearbit provides Business Intelligence APIs
Tracxn - data on 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.