I'm still mucking around with ASP.NET AJAX (get your 1.0 RTM bits here, y'all) and I needed a client-side "progressbar"-type thingie to display during AJAX postbacks. Note that I don't care much about "10% done... 20% done...", etc. I just wanted to give the user some visual indication that something's happening behind the scenes (especially since the entire page isn't visibly refreshing itself... this being the whole point of UpdatePanel and friends in the first place).

There are bazillions of Javascript progressbar implementations out there, but I wanted one that simply ping-pongs back and forth forever... that way you can show/hide it as needed in client-side code, to indicate background work of some sort.

I stumbled on Sahil Malik's implementation, which wasn't quite what I wanted, but close. He wrote a custom WebControl that allows you to specify percent complete and all that... so I modified it to do what I wanted instead.

For those who may not know, custom WebControls give you complete, well, control over their rendered output... so not only does the control emit the necessary HTML (just a table and a few columns, really) but it also emits the Javascript that does the animation. So the control is self-contained and pretty easy-to-use (IMHO).

Here's a demo, and here's the source. If you're using AJAX, try combining this with UpdatePanel, UpdateProgress and friends... pretty easy to achieve a decent user experience. Cheers.