ScreenFlow screen-casting and video editing zone
I can't begin to describe how much I love ScreenFlow. It has been my loyal ally for my work for a long time now. It does exactly what I want and need without clutter. The clip grouping and nesting, text handling, the video transition editing, export options control, and above all their super easy to use Video Action and Audio Action system, are unbeatable.
Don't compare this with tools like Final Cut Pro (which I also love for many types of projects).