IconCreator allows any picture on your machine be turned into an Icon, at the click of a button. It also includes instructions on how to enforce your Icon.
JAMESKITTY I fed the leopard version a 512 px png and it created a 512 px png file on the desktop with the icon at that size, but it failed to create the other sizes (128, 48, 32,16).
so it essentially did what candybar already does.
img2icns actually created the smaller sizes as well, btw. (Version 2.0)