When you're a trusted user, the content editors have a toolbar button that switches between text and HTML mode. The HTML mode is not WYSIWYG, but it will allow you to enter and edit HTML tags directly, or cut and paste into it from a more full featured HTML editor. Keep in mind that the editors will still post process that directly entered HTML at save time, and may strip out some things. As an example, I know they don't allow empty anchor tags.
Jamie