Yahoo Contacts allows syncing Apple's Address Book with the Yahoo! CardDAV server (and presumably others).
Synchronization Service
Memotoo is compatible with CalDAV and CardDAV.
Synchronization Service
fruux is compatible with CalDAV and CardDAV.
CalDAV/CardDAV service
Landmarks is a CalDAV/CardDAV service available initially in Germany.
E-Mail/CalDAV/CardDAV service
servermx.com offers e-mail hosting plus Contacts and Calendars via CalDAV and CardDAV support.