TinyMCE Advanced is basically a plugin for WordPress that allows you to add fourteen different plugins to TinyMCE, the editor that is used for the visual editing.
This enables toolbars and css for posts which is pretty interesting. Makes things a lot more powerful in the editing fields. You can even use the WP smilies if you wish. While it’s neat in sort of a weird way, I personally just rather use an all text editor. Just not a very visual editor type of guy.