I remember reading somewhere that wikis were ugly and after wresting with the design of my wiki I must agree.  As you can tell by my delicious links I have been on the hunt for a new wiki skin without having to do too much of the programming myself.  Reading through many comments about wiki skins it does not seem to be an easy process to totally redesign a wiki.  There are a few skins on the meta.wikimedia.org but it is not as easy as a wordpress template.  A great discussion of issues can be found at http://shearer.org/Mediawiki - the author explains that not all skins are equal.  There is a link to a tutorial on how to edit the .css file for monobook that I can going to check out.