GNOME's theme sites:
http://art.gnome.orghttp://gnome-look.org
http://art.gnome.org
http://gnome-look.org
KDE's theme site:
http://www.kde-look.org
Other Linux theme sites:
http://www.themedepot.org/http://themes.freshmeat.net/http://www.wincustomize.org/http://www.deviantart.com/
http://www.themedepot.org/
http://themes.freshmeat.net/
http://www.wincustomize.org/
http://www.deviantart.com/