Wow. It isn't often that my jaw literally drops when checking out a new piece of software... I think the last time that happened was when I first saw Google Maps. Well, it just happened again with Google Calendar.
Man, these folks know how to write software! If you haven't seen it yet, check out Google Calendar. This is a great solution to a very, very old problem. Organize events with whomever you want. All the invitees need is an email address and a browser, and they can participate.
Note that all of the intuitive things you would expect from a calendar actually work... like dragging over multiple days in the small month-view calendar to the left, and having the full view to the right automatically update to show the days you've selected. And you can drag events around on the calendar just like you would think you should. Some amazing stuff -- I'm sure it'll take awhile to learn all of the features.