Have you added a Google calendar and it’s not showing up on your Android device?
Go to Settings > Applications > Manage Applications > All
Calendar > Clear data
Calendar Storage > Clear data
Google Calendar Sync > Clear data
Then go into Accounts & sync and perform a Sync now
Your new calendar should now be visible on the device.
If you’re also syncing an iPhone, go to http://m.google.com/sync from your iPhone and select which calendars will be visible on the device.