Recently I needed an animating circular progress bar for a website I was building. After some reasonably in-depth research I couldn't find anything that entirely suited my needs, so I sat down and wrote my own jQuery plugin to do it. And here it is.
Stop reading - I've completely rebuild this plugin and open sourced it, and you can find all the details here.
It does round progress bars, both as circles and discs, and bar progress bars, both vertical and horizontal. For any progress bar there is the option to include a number to show the percentage complete, as well as some controls for altering the percentage shown (mainly for debug - I'm not sure there's a good real world application for that).
Circles
Horizontal bars
Vertical bars
It uses CSS3 for the roundness - no images, just a bit of border radius and a bit of rotating, so it'll only work on modern browsers. It's a bit slow on this page because there's so many examples running at once, but if you only need a couple of them on a page it's perfectly fine.
It's something I'd like to build on, but if you want to use it, be my guest. You can download the minified js here, which contains full setup instructions and options details. You'll also need this CSS file. I think that's it. As ever, I'll put it on github when I think the code is clean enough.