Preview the desktop with Aero Peek
You can minimise all your windows and get back to the desktop by clicking on the box on the bottom right-hand corner of the screen.
http://res2.windows.microsoft.com/resbox/en/Windows%207/main/f/6/f60c6ab8-7da5-4e90-9724-b72f9e8aed0c/f60c6ab8-7da5-4e90-9724-b72f9e8aed0c.wmv (This link takes you to the Microsoft website).