mx.controls.Image subclass that adds graphical preloading display. You can use included preloaders or create your own.
Its free unders the Artistic license. check out
Download is for flex3, flex2 available on my site.

sample:
http://strawberrypixel.com/blog/flex-components/

tutorial: http://strawberrypixel.com/blog/flex-components/preloading-image-tutorial/