It looks like Google Calendar (GCalendar) is coming really soon. The calendar.google.com domain is live now though it shows the main Google search page for the moment. I noticed this while seeing one of my website referral.
Even before the launch of Google Talk and Google Base, their subdomains went live few days before the actual launch. The same can be anticipated with GCalendar since the Google calendar subdomain is now live.
It'd be nice if Google integrates calendar into GMail. Yahoo Mail already supports calendar which can also be synched with Microsoft outlook. Let's hope gCal could be much better. Google calendar should also connect with the Calendar plugin in Google Desktop and even the TODO list plugin.