This is the radiance theme for xfwm4. It's not perfect, but fits perfectly with Ubuntu Radiance GTK theme.
It's based on radiance-xfce-lxde theme (http://xfce-look.org/content/show.php/Ambiance+%26+Radiance+Themes+for+Xfce%26LXDE?content=146674) but focused only on XFWM4.
I removed gradient from title bar, and recreated all image files by myself, so now fits perfectly. You cannot tell were title border ends, and application window starts.
Extract the folder and move it to /usr/share/themes