This is a good tip. Modifying the TinyMCE editor is great for sites where clients have limited or specific formatting needs.

In WordPress 3.9, TinyMCE is moving to version 4.0 and the above code snippet won't work anymore (at least as of testing today). Instead, you'll need to use "superscript" and "subscript" instead of "sup" and "sub."

A full list of buttons is here: http://www.tinymce.com/wiki.php/Controls