Calendaring Clients
Below are is a list of clients capable (or not!) of synchronising publicly available .ics calendar files. Please help with this page if you can - it would be excellent to know about your successes or failures
Also, wherever practicable, please ensure the refresh is set to nothing less than once a day to minimise network traffic.
I don't have Microsoft or Apple products so testing their clients (Outlook and iCal respectively) has not been possible.
Does Work
Evolution
Open source calendaring client. Works ok. Click for instructions
Google Calendars
Free calendaring client. Works ok *BUT* there remain doubts about whether calendars are always updated correctly. A discussion on this can be found at http://getsatisfaction.com/google/topics/ical_sync_does_not_refresh_at_all_or_not_fast_enough. If you go the Google route, Click for instructions
Kontact
Open source calendaring client. Works ok. Click for instructions
Should Work
Android Phones
Android phones need an app from their app store - the product page is Calendar (CalDAV) Sync for Android
Apple iCal
Should work fine but I don't have access to a Mac machine to try it out.
Apple iPhone
If you are using OS3 or above then this should work no trouble. If you were an early adopter you can always use RemoteCalendar
Microsoft Outlook
How closely MS Outlook supports caldav calendaring protocols is moot. If you have Outlook 2003 you will certainly need to install additional software to get this to work. You should have a look at iCal4OL or Remote Calendars
Outlook 2007 and 2010 should work ok, so let me know your successes and maybe supply me with some screenshots and instructions? 
Doesn't Work
Mozilla Sunbird / Lightning
Mozilla's terrible twins won't play ball on my Linux machine - I kept getting DAV_NOT_DAV errors. Let me know if you can coax some life into either of these two on Windows or Mac platforms. I suspect the problem is localised to the Linux platform so you should be ok on Windows/Mac