For example, using Google calendar (calendar.google.com), you can have a calendar and have clients get automatic updates to the calendar via RSS and email (so you have a double solution).
Microsoft's OfficeLive is another option. It has a schedule and calendar feature service. You might want to work with a local consultant to have them customize a solution for you as well.
37 signals (37signals.com) makes great tools for scheduling and project coordination.
Webex Office (weboffice.com) is a powerful intranet which has calendaring and could have the tools for you. Another tool is Catalyst web.
These are a few options you might want to consider!