KDE has enough options to make the desktop look great without any extra software. Go to settings/control centre (might be slightly different on yours). YOu can play with all of the options there. However, if you want loads of great themes/wallpapers/icons etc., go to
http://kdelook.org . Get the icon set Umicons - it's great (obviously there's loads of icon sets, but IMO this is by far the best I've seen)
Guy