Clearbit - Clearbit provides Business Intelligence APIs
Clearbit for Salesforce – Lite - Rich data on every record in Salesforce for free!
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
DiscoverOrg - DiscoverOrg is an IT sales intelligence platform providing technology marketers access to data, IT org charts, and real time projects.
RocketReach - RocketReach allows you to lookup email and phone for 250+ million professionals.
Owler - Owler is a crowdsourced data model allowing users to follow, track, and research companies.