Misleader.org

Professional Themes
Collection of several pages of themes including Ansel Adams, Anne Geddes, Norman Rockwell, Claude Monet, Paul Cezanne and others all themes include wavs and icons.
www.geocities.com/

Fermilab Themes for KDE
These themes were made for Linux's KDE Desktop. Several themes available, that includes nature, landscape and mechanical.
home.fnal.gov/

CatThief's "Mostly Crystal" themes
Themes for Mozilla, Firefox, and Thunderbird running on Windows, Linux, and Mac OS X.
www.tom-cat.com/

Envolution Themes
Demo PostNuke, XTE, Xanthia, Autotheme, PHPnuke, PHP-Nuke, Xoops themes all on under the Envolution Content Management Framework [Demo of Envolution Theme Drivers, Downloads are not activated solely a demo site].
www.envothemes.com/

The Extension Mirror - Themes
An unofficial list of themes available for Mozilla Firefox.
www.extensionsmirror.nl/

UNIX Themes - TUCOWS
Desktop themes covering Enlightenment, KDE and WindowMaker, extensive assortment of categories to choose from.
rcn.unixthemes.tucows.com/

Extreme Themes
Variety of themes and screensavers for download, and Web and graphic design.
www.extremethemes.net/

PC Themes
Custom desktop themes and screen savers for advertising and marketing using wallpaper, sounds, icons, cursors, mouse pointers, skins, web views, startup and shutdown screens, font and color settings.
www.pcthemes.com/

Themes.org
Site provides the Linux and UNIX community with the highest quality repository of graphics, and the central resource for themes. No matter what your personal tastes, or current mood is you will find a theme.
themes.freshmeat.net/

Aqua GTK gtk.themes.org - Theme Gallery

gtk.themes.org/