I like changing my desktop wallpaper very often, especially when my sight falls on something worth keep looking at all the time, yes , some designers and photographers’ works are astounding and astonishing and I am sure nobody minds adding some refreshing, vivid elements to his workstation
here are some site which have nice wallpapers and themes you might be interested in
www.customize.org for art, wallpapers, themes and styles.
www.deviantart.com for everything
www.iconspedia.org for icons