I'm a big fan of James Hollis' blog, Teachers Love SMART Boards. I emailed James to ask him about the Sketchcast.com website, which seems to have disappeard from the internet, and to tell him about my idea for using the Jing Project as an alternative.
He in turn told me about Freescreencast.com which, like Jing, will allow you to record and then upload a screencast for free, and then to embed that recording in a blog or wiki.
I just looked at the site briefly, and it seems like a winner! Here is a sample screencast that James Hollis created with FreeScreencast: