Calendar backup while away from time machine I am occasionally away from my time machine disk. During these periods I would still like to backup my calendar in case the hard disk (MacBook's) crashes.

Which file or directory should I copy to backup iCal's entries?

Edit

I am looking for a maintenance-free backup method (i.e. one that does not require me to think about it until something bad happens).

Might it be possible to sync iCal with a cloud-based (perhaps Google's) calendar? Is it possible afterwards to sync back into iCal?
If you are running Lion, iCloud, launching in October 2011, will soon provide cloud-based back up for calendar information.

To manually backup iCal entries, Apple recommends that you either


Save an iCal Archive on your hard drive (File » Export » iCal Archive...)
or
Export an individual calendar to a file on your hard drive (use this method for any CalDAV calendars) (File » Export » Export...)


To protect against hard drive failure, copy the resulting files onto external media.

If you wanted to sidestep the Apple recommended process, and simply back up a single folder, it appears your calendar data files are stored in ~/Library/Calendars

Additionally, Google provides instructions for how to sync iCal with Google Calendar.