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.
fruux - Free service that takes care of your contacts, calendars and more so you don't have to.
GlipMe - GlipMe is a cloud based address book to manage personal and business contacts.
FullContact - Put the power of full contact information into your web or mobile apps.
Pobuca Connect - Connect with your contacts.
Funambol - Funambol is the leading provider of platforms that power many cloud services.