Show Desktop is a free portable tool which allows you to get the show desktop button in Windows Vista & XP. You can also use it in Windows 7 because it has more customization features. In Windows 7, if you increase its width, the original show desktop button will be there making it look ugly so you can use Windows 7 Show Desktop Button Remover to get rid of the original button.
How to use:
Just run the tool and you will be able to see the new show desktop button. To customize its settings, right-click on the button and select Settings.