fruux - Free service that takes care of your contacts, calendars and more so you don't have to.
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.
Free Address Book - In our contact management software you can store fast and easily name, phone numbers, birthdays, address, company name, city, mobile numbers, insurance and loan info, e-mail addresses.
Funambol - Funambol is the leading provider of platforms that power many cloud services.
Clearbit - Clearbit provides Business Intelligence APIs
Kontact - Kontact is the integrated Personal Information Manager of KDE.