Give your eyes a soothing relief from your long daily work schedule. Have a look at these wonderful images from the Earth Day photo contest organised by Bing. You could also use these images to set them as your wallpaper or use them as a Windows 7 theme.
You can download the theme directly from this url. You can also read more about building your own customised theme in Windows 7. The photos in the theme which act as background images are shot by students from kindergarten to college shot to help educate the world about Earth Day as the part of a contest held by Bing.