• Google Calendar for Lesson Planning
• Totally Awesome, or maybe a little creepy - Google will find events in your email and add them automatically to your calendar. You can change this in your settings, but then you just don't see the creepy...
• Create Appointment Slots - Great for setting meeting times or also for reserving shared resources like a laptop cart or computer lab. This only works in Google Apps for Education (or business) and not for a free gmail account. (tutorial video)

Stuff You can Do with Google Calendar:

• Can have multiple calenders each with different sharing preferences
• Alerts - Never forget an appointment gent an alert via email or pop-up.
• Google Now - Also a bit creepy.
• Sync with Outlook, iCal, Mobile devices
• In Apps domain you can use it to schedule resource or space.