Ahh, Google and Mozilla, two wonderful companies with wonderful products that compliment each other very well; and the best part, they are free.
For awhile I was using Apple's Mail and iCal, now they work very well, but I needed something that synced with Google calendar better.
That's why I switched over to Mozilla's Thunderbird with Lighting.
Syncing Google calendar with Thunderbird is a breeze.
First thing first, get the Lighting plug-in for Thunderbird.
Lighting allows you to use a calendar feature in Thunderbird, making Thunderbird now function like Microsoft Outlook or Entourage.
Now you will need to get access to your Google calendar, for this you will need another plug-in for Thunderbird: Google Provider, this allows you to access and edit your Google calendar in Thunderbird.
Now that you have these two plug-ins, we have to get your Google calendar in Thunderbird.
1. On the Google Calendar web site go into Settings in the top right hand corner.
2. Select Calendars.
3. Select which calendar you would like to sync with Thunderbird.
4. Once in the desired calendar scroll down to where it says Calendar Address. To the right will be a orange button that says XML, select it.
5. Once you select the XML button a pop up will appear that will have a URL in it, select and copy the URL then click OK.
Now it's time to go into Thunderbird.
6. In Thunderbird's menu bar go to Calendar - New Calendar.
7. A pop up will appear, choose On the Network, then Continue.
8. Choose Google Calendar for the format.
9. In Location paste the URL you copied earlier, then Continue.
10. Now name your Calendar, select what color you would like it to appear as and choose if you would like alarms, then Continue.
11. Click Done.
Now your Google calendar appears in Thunderbird; and if you make a change to the Calendar in Thunderbird it will also change it on the Google Calendar website.
You can also use this as a Mobile Me alternative for managing your calendars, check this tutorial out to see how to get your phone involved as well.