Plaxo – Online Address Book and Contact Management

Excellent web-based Address Book and Calendar service. Plaxo lets you get all of your contacts, calendar entries and address books to one place. Syncs with: Microsoft, Google, Yahoo!, AOL, Mac, Thunderbird, and your mobile phone.

Free Account Features:

Sync. Plaxo Address book and Calendar with Outlook, Google, Yahoo, Hotmail, AOL, Mac, and other popular tools.
Automatically updates your contacts’ details as their info changes.
Sync. your notes/contacts/calendars across multiple computers (work, home, college, etc.).
Share your contact/s with others.
Ad notes, Birthday reminders.
Integrated ToDo list service.
Extra features that come with Premium account (49.95$/year): Backup and recovery, mobile access, 24/7 live support, etc.

Plaxo introduction and demo video