There are a lot of WYSIWYGs plugins and scripts out there but most of them are not that good. If we take a look at big sites like GitHub, Stackoverflow and more, we can see they are starting to use Markdown as they editing option.
EpicEditor is highly customizable and provides a cool set of options via a full API. You can make it load or import data, save or export HTML and many more. Theming is quite easy and only requires two steps (more on this on EpidEditor website).