Google has finally opened up CalDAV support in Google Calendar. Simply put, this means Apple iCal and Google Calendar can sync with each other directly now. There's no more need for a third party tool like spanning sync.
So far, the syncing works really well. My Google Calendar shows up as a new calendar in iCal, and any edits and additions I make to it in iCal show up a few minutes later in Google Calendar. There are some limitations to the service, but none of them have been an issue for me in regular use.
Instructions on how to set this up can be found in the Google Calendar documentation.