Clearbit - Clearbit provides Business Intelligence APIs
fruux - Free service that takes care of your contacts, calendars and more so you don't have to.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
FullContact - Put the power of full contact information into your web or mobile apps.
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 Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.