Windows only: Have your calendar available on the desktop as well as in the cloud with the Google Calendar Sync desktop tool, freshly released from the big G. Sync your primary calendar on your vanilla or Google Apps account to Outlook automatically at a refresh rate you define. Syncing can be one- or two-way, meaning you can add and edit events in Outlook and have them sync to GCal or vice versa automatically. The only catch is that it only works with your primary calendar, not secondary ones. Google Calendar Sync is a free download for Windows only. (Of course, having Outlook helps.) This coupled with Gmail IMAP really makes Outlook a viable GApps client.
