What calendaring systems are church websites using?
A quick google search reveals some church calendar vendors like http://www.mychurchevents.com/ and Connect Daily. I'm sure many others are opting for the free Google Calendar, which has a nice API. (here's a tutorial on how to integrate a Google calendar to your church website)
Still others are using a custom calendaring system provided by the Content Management System from their website's provider. And I'm sure there are also many folks who hacked together their own calendar from some open-source codes/frameworks.
What are you using, how much are you paying (if anything), and are you happy with your online church calendar? As always, will update the post with examples cited in the comments.

We're set up with Google Apps, so we use it for email, calendar, and our website via Sites. Google apps is free for non-profits. We can create different calendars and assign different colors to those calendars and who can update them. The aggregate them for display.
Posted by: Ben Hunsberger | September 04, 2009 at 05:44 AM
Joe, we're using the calendar feeds from our scheduling software from ACS. It's called Facility Scheduler. It's got a long way to go before I'm 100% happy with it, but it's far and above better than anything we've used in the past. We now have one calendar that rules them all. ACS provides APIs to get the event data, so that means that I can run an Energy Management System with it, push it to screens in the lobby, have it synced on the Web. Make one change, and the event is changed everywhere it's published.
Posted by: Matthew Irvine | September 04, 2009 at 09:19 AM
I'm the lay web guy at my small church plant and we simply use an embedded Google calendar. Free and works like a charm.
CityWest Church
http://www.citywestchurch.com.au
Calendar:
http://citywestchurch.com.au/resources/calendar/
Posted by: LayGuy | September 07, 2009 at 07:38 AM
We have been using the Mychurchevents for a while on our site, but are not that excited. You can embed an upcoming list of events, but not the entire calendar. Also, it's not as clean as Google. We are considering moving to Google, or another resource.
Posted by: Billy Taylor | September 22, 2009 at 12:18 PM