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.
Truecaller - Find a person by a name or phone number worldwide for free using Truecaller.
ThisNumber - ThisNumber helps you find phone numbers for people and businesses!
Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.
Sync.ME - Search over 1 Billion phone numbers worldwide. Identify unknown phone numbers and block unwanted calls.
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts