To add a nice hover effect to the icons in the stacks pop up enter the following code into your terminal ( applications/utilities/terminal.app)
defaults write com.apple.dock mouse-over-hilte-stack -boolean YES killall Dock
To Remove this Stacks hover effect enter the following terminal command:
defaults write com.apple.dock mouse-over-hilte-stack -boolean NO killall Dock
Here’s a preview of the magic at work.It’s also important to note that this only shows when you navigate your stack pop up by keyboard.

If you would like to set a specific icon for each stack instead of the default stack pile of icons, Stacks in Da Place from Eagle-of-liberty was developed with you in mind, It’s a great little piece of donationware that lets you use any icon you want for any stack, easy as dragging and dropping the icon you want.

Download Stacks in Da Place at the developers site - Click here to Visit
I find Leopards new Stacks feature incredibly useful, and fun to watch at the same time! Here are a few tweaks to help you make the most of stacks.
You can add a ” Recent Items” Stack to your dock by entering the following in terminal ( You can find terminal in /applications/utilities )
defaults write com.apple.dock persistent-others -array-add '{ "tile-data" = { "list-type" = 1; }; "tile-type" = "recents-tile"; }'
Once the stack appears you can right click it and select its type, and a few other features. To add a nice hover effect for the icons in a stack when expanded, Enter this line into the terminal
defaults write com.apple.dock mouse-over-hilte-stack -boolean YES
Type the same, with NO at the end to reverse this effect.
If you don’t like stacks and the reduced folder browsing capabilities, you can download Quay, Developed by Rainer Brockerhof, It Allows you to add your drive, or folders to your dock and browse them via a menu just as you would in OS X Tiger.
