Website Recomendation
For the last few months we've been using Airset as a family calendar. It allows multiple group creation, has to-do lists, contacts, and even a blogging system. It'll send daily reminders as e-mail or SMS, and a daily itinerary for the next day, or you can get upcoming events by RSS.
The UI is full of AJAXy goodness, you can sync with Outlook, and it's free.
On the other hand, Google is supposedly releasing a calendar application soon, and when that happens I'll probably dump Airset.
Life's funny that way.