Cardhop - The Mac contacts app you'll want to use.
The Contact Guru - Managing your contact list 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.
ContactRescue - Magically get your address book up-to-date and accurate
Webby - Webby allows to use Facebook, Youtube or any web app as a regular desktop apps, integrated with the...
Followup.cc - FollowUp for email is a lightweight productivity suite that keeps your conversations and tasks from slipping through the cracks. Set perfectly timed reminders that arrive at the top of your inbox, right when you need them.