Somehow, having a beautiful desktop wallpaper makes working at a computer all day a little easier. Here are some great places to find beauty without the risk of accidentally getting unwanted malware...
The Desktop Wallpaper Project: http://www.thefoxisblack.com/category/the-desktop-wallpaper-project/
DMB (Dual Monitor Backgrounds): http://dualmonitorbackgrounds.com/
Social Wallpapering: http://www.socwall.com/
Desktop Nexus: http://www.desktopnexus.com/
Good Fon: http://www.goodfon.com/
Pixelgirl Presents: http://www.pixelgirlpresents.com/