Soon after releasing offline access for GMail, Google now makes available offline Google Calendar. It was previously only available to Apps users but has now been turned on for everyone. Like offline GMail, offline GCal uses Gears to sync while online and make content available locally when offline.
The neat thing about this is that you can now have access to your schedule/agenda while on the go, and all in one place within GMail if you have enabled the Calendar gadget.
The downside is that calendar entries cannot be edited while offline for automatic syncing when you get back online. Hopefully this is a feature that will be introduced soon.