I found a good looking WYSIWYG mediawiki editor called extension:WYSIWYG here http://www.mediawiki.org/wiki/Extension:WYSIWYG
Unfortunately, this version is not supported on mediawiki version 1.18 yet. I tested it myself; it really does not work on 1.18.
In the extension’s discussions I found that someone has modified it and posted it to: http://wiki.linuxmatter.com/index.php/File:WYSIWYG.zip
I have tested it. It works fine with version 1.18