Cardhop - The Mac contacts app you'll want to use.
Bond - A simple app that reminds you to keep in touch with people
The Contact Guru - Managing your contact list so you don't have to
Thankster - Automagically send hand written cards
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.
Thankbot - Drive more business with handwritten notes