Magic Eraser uses... did you know you can cut a piece off and float it in your toilet overnight and voila! no more toilet ring! -clean window screens (even when they are still in the window) The website has a list of about 100 uses!
If you have a stubborn toilet bowl ring, cut off a piece of a Mr Clean Magic Eraser and let it sit in the bowl overnight. Magic! You will have to scrub it a bit though