I recommend CKEditor(
http://ckeditor.com/[
^]), which is highly customizable.
The thing you try to do, is not built-in in almost any WYSIWYG (What You See Is What You Get) editor out there. Thus, you should implement it on your own. But by using a third-party WYSIWYG, and customizing it (instead of creating a WYSIWYG editor entirely from scratch), you can get sure that you already have tens of other functionalities.
Also I should note that most WYSIWYG editors can become as simple as having one toolbar with basic formatting buttons