Try Remember The Milk Web Organizer
Web application useful, but not for calendar or organizer. That’s my opinion. The reason is simple, calendar or organizer should can seeing every time.
Use calendar or organizer web application make us have to online every time we need to see it, something that I can not do. But, my opinion above changed after I try services from Remember The Milk (http://www.rememberthemilk).
This site services is interesting because it support Google Gears. So it can be use while offline.