Screencast-o-matic. SOM is very easy to use. Go to their website, select "start recording", choose your screen size, record, and you are done. Files can be saved to your computer, uploaded to screencast-o-matic, or uploaded to YouTube. You can record up to 15 minutes.
There is a number of ways in which screencasting can be used in the classroom. The obvious way is to record lessons to have available for students to watch on their own time. Students can also use SOM to record presentations. The teacher can also use SOM to record how to use a piece of software or web application. I have also seen screencasting used to give feedback to students on their projects or papers. Giving oral feedback is much more beneficial than the dreaded red pen. Give it a try today.