Giant Robot

Paul from MiC requested a font size selector in his WordPress TinyMCE config. Turned out to not be so hard after all ... this change was to WordPress 2.0.4

1. Edit wp-includes/js/tinymce/tiny_mce_gzip.php
2. Find the line which contains $mce_buttons = apply_filters('mce_buttons', array( /* lots of options here */ ) ;
3. Insert your new buttons into this list - for me this meant adding 'fontsize_select', 'separator' after the first 'separator'.

Simple ... but also worth documenting as there seem to be a few questions on this topic around. LucidGreen has a post on further WordPress TinyMCE customisation too.