This is border line between something really cool and an animated .gif you might find on geocities (now myspace), but I’m going to mention it, anyway. It’s a plugin called busy_ajax. What this does is put an ajax spinner wherever the mouse is during an ajax request.
It’s cool that it handles all requests for you, so you can eliminate keeping track of that dom_id variable. But at the same time, since it’s a wandering animation, it can arguably be labeled as cheap and unclean.