Sync Google Calendar with Apple iCal via Spanning Sync
iCal and Google Calendars are great applications for different sets of reasons, one is online with sharing capabilities, one is desktop driven with great notifications and offline capabilities. Get ready to get excited Mac users, Spanning Sync syncs all of these features together and lets Mac users choose which calendar application you want to work in with total two way calendar synchronization.
If you find yourself working on different Macs, or require a calendar that is shared throughout the day, Spanning Sync ties in support for multiple Macs and sharing capabilities. Simply share a Google Calendar, and Spanning Sync will sync them all together. Changes made in iCal, will appear on the Google Calendar, and changes that are made to Google Calendar will be made on the iCal calendars. Apple's iSync then works to sync up calendars onto capable devices like mobile phones and iPods as well.
There is a 15 day trial period for Spanning Sync, with a one year subscription costing $25, or you can drop $65 to purchase the app outright.