I don't have any personal suggestions, as I've not really had to deal with this. For me, the ideal application would be one which outputs well-structured, semantic, valid HTML with plenty of ID and class attributes in the tags, allowing me to apply my own CSS stylesheet to the resulting pages. As to which ones (if any) do this, I do not know. It might be worth your while to narrow the search on "skins" or "skinning", to find those that have some sort of built-in mechanism for customizing the appearance.