Screencasting is a great tool for a number of reasons. Whether you want to show a route on a Google map, have students explain their work, or demo a new web tool with instructions for other staff or students, screencasting can be really quick and easy. A newer tool that is great because you don't have to download anything is Screenr. I also like Jing.
Both of these tools allow easy posting to a website or Youtube. Both are free and easy to use. See my last post on Math tools for an example. I used Jing on that one.