Included with Mac OS X 10.6
Desktop client for Mac OS X that supports CardDAV. Also provides CardDAV-based auto-complete to other apps via built-in APIs.
Included with iOS 4
Client for iPhone/iPod Touch that supports CardDAV.
Included with Atmail 6 Product PHP/Zend, jQuery
Supports CardDAV to list, view, edit modify contacts directly from the server.
Open Source/Cross-platform
Desktop client that supports CardDAV.
Free/Windows
Desktop client for Windows (.NET) supports CardDAV.
Free/Thunderbird Plugin
Plugin for Thunderbird address books which allows CardDAV subscriptions.
Android sync adapter
CardDAV-Sync is a sync adapter for Android devices that synchronizes contacts via CardDAV. See https://market.android.com/details?id=org.dmfs.carddav.sync for ratings.
Available in free and purchased editions
Open Source CardDAV client
Desktop open source client (Javascript+jQuery) for CardDAV.
Open Source CardDAV client
PHP CardDAV Client.
Open Source CardDAV plug-in
Open source CardDAV plug-in for Roundcube Webmail.