The new Google Calendar is impressive in terms of simplicity and ease of use. Pretty cool AJAX tricks as always. Definitely worth a try, but be warned: You will be amazed, and won't be able to get away from it.
One cool trick I found was you could specify the time of the event in the event name like this: "Dentist Appointment at 7:45". Google Calendar is smart enough to recognize 7:45 as a time and set it appropriate for you. Neat!
You can check out the new Google Calendar at calendar.google.com.