I like the Google Calendar interface. The most useful feature beyond sharing calendars is the SMS notification.
I also use Thunderbird and was looking to tie it all together. Using Lightning and the GCal provider, I now can synchronize my calendars (in an open way). The setup is very simple. Here are the pieces that make up the solution:
- Mozilla Lightning for Mozilla Thunderbird 2
- Provider for Google Calendar
- Instructions on how to synchronize with Google Calendar or LifeHacker instructions
Image: courtesy of LifeHacker