Calendar sharing is hot nowadays. My wife and I are using Google Calendar
to share our agenda. In the past we didn't really manage our common appointments and that resulted in all kinds of misunderstandings. With Google Calendar we've found an easy way to organize our "life" : birthdays, family events, holidays, ... we like it : it looks good, it's fast and we only need a browser to access our agenda from everywhere!
I'm also impressed by Outlook 2007
lately. I'm using Office 2007 on Vista quite some time now and I would certainly recommend it for a bunch of reasons. One of the cool new features of Outlook 2007 is to publish your calendar to Office Online (Internet Calendars) and to share it with the people you want. Another possiblilty is to send a custom snapshot of your calendar by mail to anyone you want.