I just came on another Xfce theme, complete with xfwm4 theme. Dark Standards is supposed to be a combination of the default Xubuntu Studio theme and the standard Xubuntu theme.
Here's a screenshot of Dark Standards on my laptop. The icons are the default Xubuntu Elementary Dark. The wallpaper is Xubuntu Karmic wallpaper, which is available as an option in the Xubuntu 11.04 Desktop settings.
Dark Standards Xfce-Look.org