
The default menubar clock on Mac OS X is quite limited. I would expect a calendar view to pop-up on clicking the clock but that is not the case. All you get are the choices shown left. To get a calendar view, you have to click "Open Date & Time" and even n you don't get a good calendar view and it is quite easy to accidentally set the system date while you are clicking about. Thankfully there are quite a few alternatives.
Also the only one with a paid version which unlocks even more features. But annoyingly it has a dock icon which is almost unpardonable for an application which lives exclusively in the menubar. When you are cycling through your applications using Command+Tab it is an extra icon which you need to ignore always. Even more annoyingly, if you select the icon when cycling, it will open the calendar view. When an icon is present always in the menubar, the logic of adding an icon to dock escapes me. If you are willing to live with these, it is a feature rich application. The paid version can sync Birthdays from AddressBook into iCal and has a configurable Hotkey. The app can show events from your ical calendars. All dates with events are highlighted. Clicking on a date will open the events view below the calendar. Clicking on the Month name, will show all the events scheduled for that month. But even if you have an event scheduled for the current day, opening the calendar view does not open the event view automatically forcing you to click the date to see if the events. Also the difference between a current date highlighted without events and with events is subtle and causes confusion. You will have to click the date to be sure.
Instead of a displaying time like "10:28" like other apps it can display time like "Half Past Ten". The calendar display is nice and compact and clicking on a day will open iCal with a view of that day. When you hover on the calendar view, a small i appears on the lower right hand corner of the calendar.Clicking on it will get you a menu with an option for "Preferences". The only issue with Magical is that, if use spaces it opens the calendar in the original space it opened in and not in the current space.
But unlike the other two apps, clicking on a day will not open iCal for you. The calendar is a bit easier to navigate than others, as you can advance the calendar by month or year.Magical's issue of not opening in the current space is a deal killer for me, so my vote goes for eigenclock. Eigenclock does not privide a way to launch it automatically on login, so you have to add it to Login Items for it to launch when you login. Login Items can be accessed via System Preferences -> Accounts.
Also the default menubar clock can be disabled and enables from the system preferences panel. System Preferences -> Date & Time -> Clock.
For such a basic functionality it is a pity that we ahve to rely on third party apps but if it is any solace the options available are pretty good. Hope that Apple adds some more features, especially the calendar view to the menu bar clock.