With autumn leaves falling outside, you should have leaves on your desktop. One of the coolest programs around is AutumnLeaves which causes leaves to tumble down and collected on the tops of your windows. The occasional falling nut and growing mushroom adds to the wet and cool feeling of a chilly autumn morning. It's shareware and worth paying for.

And, to add to the autumn effect, use one of these images ( 2048x1536 , 1600x1200 , 1024x768 ) to complete your leafy desktop.

By the way, the AutumnLeaves author also has Snow for Windows and Hanami (falling cherry blossoms) so you can enjoy all of the seasons.