Cobook for Mac
The Mac OS address book is lame to say the least, but the free Cobook is most certainly not. A massive improvement.
"Cobook knows what you mean. Just type in an email, phone or other piece of info and Cobook will sort out where to put it. Cobook keeps your contacts up-to-date. Connect your social network accounts and Cobook will automatically look up pictures, companies, phone numbers and other contact details."