If you've grown fond of the Windows 7 "show desktop" button and would like the same button in the same location (beside the clock and system tray) on Windows Vista and XP, Show Desktop helps preserve interface continuity across all your desktops.
Windows XP and Vista both have shortcuts you can place in the quick links bar to show the desktop (and shortcut lovers will of course already be using WinKey+D to minimise all windows). For users who want GUI consistency across all their workspaces, however, Show Desktop puts the show desktop button for Windows XP and Vista in the same spot it resides in for Windows 7.
Show Desktop supports Aero for transparency when used on Vista. You can enable and disable transparency, tweak the width, and change the button function from minimising all windows to toggling the desktop. Show Desktop is free, Windows only and requires Windows .NET 3.5.
Show Desktop [Deviant Art]