Need to show something to someone? iShowU is your answer! iShowU is designed to record anything on your screen, instantly - both audio, and video!
If a picture is worth a thousand words, then a movie is worth a million. Imagine the time you'll save writing Grandma an email about how to magnify her dock when you can just shoot a movie in seconds.
I've been mulling over doing a screencast so I made a small survey looking for the best choices for Mac screencast apps. This is not a review since I haven't had time to actually try them all out. But if you're looking for what's available and some links to useful reviews, this is a good starting point. Screenflow and Snapz Pro seem to be excellent choices although I had people recommend iShowU and Zing to me as well. I tried iShowU and wasn't too impressed. I tried Screenflow and thought it was pretty amazing.