Movenote is a nice, web-based video creator app that allows you to easily add video of you speaking along with an image or document.  You can easily share out directions on how to do something or even provide feedback on an assignment for a student.  Emails or text can only convey so much, adding a bit of video to the mix can help you communicate out your message much more effectively.  What is really nice is that it is integrated with your Google Apps account making it easy to create and there is even a way to integrate it with your Google Mail.