When I'm not doing CAD work, I can usually be found taking photos. This page includes some images I've taken that I think you'll enjoy using as wallpapers for your desktop.
To get the image you want, just click on the size of your screen resolution below the images. The image will appear in a new window. Right click and choose "Set as Desktop Background" (if you are using Firefox) or "Set as Background" (if you are using IE).