Most of the preloader solutions I've found on the web display the loading progress by drawing a line, sizing a block or updating a text field, based upon a percent loaded calculation. Now these solutions work just fine but I think they miss a trick. Flash has it's roots in animation so why not add some visual flair by letting Flash do what it does best.
Customising the look of your animated preloader
One simple change will give you complete freedom over the look of your preloader. Create 100 frames inside your preloader graphic and draw anything you like in those frames. If we take that same percent loaded value we can now use it to jump to any of our frames within the preloader. The example above uses MainPreloaderCentred.as, a customised version of the MainPreloader.as class I posted yesterday. This one keeps the preloader graphic centred on the screen at all times, adds some textual output and most importantly uses the animation method outlined above.
The ZIP file contains both versions of the preloader class and the FLA contains two preloader graphics to play with: A standard bar and the circle version shown in the demo above. You can use any graphic you like so long as it's 100 frames long and you remember to name it 'preloader'.