Google just added CalDAV support to Google calendars, here’s a tutorial on how to synchronize Google Calendars on iCal without any third party application or plugin installed:

1. Go to preferences from iCal and select the “accounts” tab
2. Click the “+” button to add a new account
   
3. Fill the pop up with these informations:
   Description: This will be the title for your CalDAV calendar list
   Username: The complete email address you are using with Google Calendar (example: steve@gmail.com).
   Password: The password you are using to sign in to Google Calendar.
   In the Server Options drop-down, enter [ https://www.google.com/calendar/dav/ [ your Google Calendar email address ] /user ] as your Account URL (example: https://www.google.com/calendar/dav/steve@gmail.com/user)
   
4. Then click on add and wait a few minutes until your calendars are completely synched to your Mac; all subsequent syncs are instantaneous.
   

Posted in Address Book, iSync & iCal, Macintosh Tips & Help