Calaboration

Calaboration makes it easy to set up iCal to synchronize with your Google Calendar calendars. It automatically finds all of your calendars and allows you to add any of them to iCal with the press of a button.
Due to limitations in iCal's CalDAV support of read-only calendars, Calaboration will not allow adding them to iCal by default.

To add read-only calendars despite the limitations, you can enable them from Calaboration's preferences.