Following the trend of the other Google Apps, Google Calendar is easy to use and very easy to share out with others.  You can create a calendar, which can be edited anywhere you have an internet connection, which can easily be shared with others using email or by posting the link somewhere.  You can create a class calendar that can contain the outline of each class, and even include any attachments or links for resources for the day.  It can be shared with students and parents alike.  This is another way to increase the communication in the classroom in an efficient and effective way.