The winner of last week's Android Arena on All About Android is 12Hours, an app chosen by Gina Tripani. 12Hours is a very simple analog clock widget that integrates with your calendar. It blocks out the hours where you have appointments scheduled right on the face of the clock. This is a great visual indicator of your schedule, and how long you have until the next appointment.
Once 12Hours is installed, just add the widget to your home screen and it will automatically prompt you to ask what calendars you want shown. You can even use the colors associated with those calendars. There are also a few different clock face styles you can choose from.
For Gina's demonstration of 12Hours, check out All About Android episode 144