Here there is a theme for your GNUstep Apps. Mainly this theme are for people that use desktops like Gnome, KDE, Xfce,... Just untar the package and copy it on ~/GNUstep/Library/Themes at your home directory. You can set the theme with SystemPreferences.app.
GNUstep SVN Themes
GnomeTheme is a plugin to make a GNUstep theme based on the active Gnome theme. Is under development.
The GnomeTheme has recently been renamed Gtk.theme since it really is a Gtk theme. It is available in GNUstep's SVN repository under the plugins directory. Check it out here:
WinUXTheme is the theme for Windows. You can active this on installation or with SystemPreferences.app.
You find more at GAP.