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.
Phone2Location - Caller ID, phone number tracker, call blocker, contacts location, works offline
Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.
Call Notes Pro - Call Notes Pro helps you to identify who is calling you. You won’t have to ask yourself “who is it?
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts