Drupal - Adding CSS classes to wysiwyg

Ckeditor uses the ckeditor.styles.js file to define the available styles in the Styles drop down. Documentation in that file states:

'Styles' button is not enabled by default in DrupalFull and DrupalFiltered toolbars.

If you look at the file, it should be fairly straight forward to modify it using the given examples.

The ckeditor.styles.js file can be copied to a directory accessible by Drupal and modified to include your styles. Then you have to configure your CKeditor profile to point to the new file, including any applicable CSS.