Just ran into a cool site that provides a variety of images that show busy status, which is more and more common for Ajax applications. The app lives here:

 http://www.ajaxload.info/

This isn't the first site that collects these various Loading... style images, but what nice about this one is that you can dynamically build the images by specifying colors and background colors and transparency which means you can create images that look good on any kind of background without color bleeding. It looks like this tool rebuilds the images entirely so transparent images look clean no matter what content you stick it ontop of.

Very cool idea. I've already used a few of these to retrofit existing animated gifs and ended up with smaller gifs to boot.

Bookmarked!