You could go to Box-Look.org for extra Openbox themes. There is a fair selection, although Openbox being a lightweight window manager, it doesn’t have the amount of eye-candy that Gnome or KDE have. I did find an early attempt at the Ubuntu Light (Ambience) theme, Ambiance Cold Box by GhostAssassin, which works.
I did discover from Urukrama’s blog under the Openbox Guide there is a .deb package containing a stack of Openbox themes directly available from the Ubuntu repositories. This has been around since Ubuntu Hardy. A quick search in Synaptic on openbox-themes should bring up the package in the list. Mark for install, apply, then fire up Obconf Openbox Configuration Manager and you have a selection of extra themes, some of which are moe attractive than others. RC