Jing is a great way to make a short video of screenshots on your computer.  It's free and works on both a MAC and a PC.  Once you create the video, you can upload it onto Screencast and give your clients, students, or coworkers links to the video. I use it for my coworkers when I'm creating job aids for what I do.  I also use it for my staff so that they have job aids for what they need to do even when I'm not available.  Here is a screencast I made for new workers that I hire to get them familiar about the university.

I tried out iMovie for the first time in a course in the Summer of 2011.  It's a great tool and very easy to pick up and utilize.  Below is the production of my trial.  In the course, we were given a story and then asked to finish it.  The narration at the beginning is the story that we were asked to complete.  While the story line and the cooking show are not serious, I noticed that iMovie provided me with lots of options.  For MAC users, I definitely suggest using iMovie.  It's free, easy to use, and easy to export into YouTube.