Some dark themes.
Great selection of dark zetaboard themes available at
Some lighter zetaboard themes.
The same place has a nice selection of light themes, complete with previews.
Even more Themes and skins!
Zetaboads.com has a very huge and great selection of Light, Dark, Mixed and themed themes. This is probably the best place to go for skins and it will be the best updated.
Good theme makers are hard to find.
If you can't find something to suit your skin needs in the links above then chances are it just don't exist. Perhaps ask over on the zetaboards forum and see if someone is willing to make that perfect theme thats right for your site.