When you create a new stack (really a folder) on the dock in Leopard, you end up with an icon that doesn't really tell you what is in the stack. But there is a trick that allows you to change the icon of a stack on the Dock. It turns out that the dock will use the image of the first listed entry in the folder for the given stack. So you can find an image you like (I think it needs to be in .png format) and give it a name so that it always will be shown first (I use the name 00-icon.png) and put it in the folder that the stack is for. Then right-click on the stack icon and select "Sort by" and choose "Name". The dock will instantly update to show the new icon that you have put in the folder. Very neat.