YUI has become my new favourite Rich Text Editor and I have been implementing it left right and center. It's extensability, features and ease of use are unparralled. It made sense for all these features to be available to me in MovableType also but no-one seems to have yet done that. What choice did I have but to do it myself?
This plugin adds the YUI editor to your MovableType installation as the main tich text editor, so you get something like this in yout MT:

It's an easy install, and has a few configuration options which are accessed from the plugin settings for each blog on your installation.
There is a
feed and a
category to help keep up to date, use the posts on the left to get the latest version.
Features
- Places the Yahoo User Interface Rich Text Editor into your MovableType Installation
- Generates XHTML markup (markup can be changed via config)
- Uses default Movabletype asset management but this can be disabled through config
- Allows admins to extend the YUI Editor without changing plugin code, via config
- Full screen view and HTML code editor added to the default YUI options
- Doesn't change either YUI or MT so won't affect customisations you may have made
- Can use either Yahoo! hosted JS and CSS files or your own local copy of the build folder
- Can generate suggested tags for your entry based on the content
Install
- Download Zip file
- Extract into your MT installation root, keeping folders
- Edit your mt-config.cgi and add "RichTextEditor YUIEditor" to the end or use the Rich Text Editor Selector Plugin
- To enable the auto-tag button you will need to get a Yahoo! appid from https://developer.yahoo.com/wsregapp/. You will only need the "Generic, no user authentication required" option.
Most users can stop there, if you wish to make further changes, see the "Configuration" section
Upgrade
To upgrade, make a copy of mt-static/plugins/YUIEditor/config.js before uploading new version. Then reapply the contents of afterYUIInit() but do not re-insert the configuration variables.
There should no longer be any changes to config.js in the development of the software, it will still be published with each version, so remember not to upload that file with future versions.
Configuration
There are a few options available in the blog plugin settings page to change your installation of the plugin, also in /plugins/YUIEditor/config.js is the ability to add your own customisations to the editor based on standard YUI code. There is a function (afterYUIInit) that allows you to do your own edits to the YUI Editor. A reference to the editor is created for you by default under the name "YUIEditor". There is an example in the config for adding a button, and further examples of all you can do with the YUI editor can be found on the YUI Rich Text Editor website.