Alex Bosworth has written a very simple yet effective Throbber. It’s displays nice aninmated graphic inside the browser, when data is being fetched. The browser throbbing can be a subtle expected queue, and it’s the only thing visible across tabs, so it can be nice to be able to toggle it on and off. The problem is that there are very few ways to make that happen. This method uses a hidden iframe, which increases load across the server but achieves the desired effect.
More info: Sandbox