I\'ve written a custom plugin for CKEditor--successful on all fronts, save one currently: I can\'t, for the life of me, figure out how to customize the image on the button
To add your custom icon you need to edit skins/moono/*.css For the editor itself you need to add the same CSS class in the following files
The format name for a CSS button class is .cke_button__myCustomIcon_icon
You can either use your own image file for the icon or edit the sprite /skins/moono/icons.png to add your's.
In your plugin.js you need to have something like
editor.ui.addButton('myplugin',
{
label: 'myplugin',
command: FCKCommand_myplugin,
icon: 'myCustomIcon'
});