Code by @alisothegeek to enable a styles dropdown in the WP tinymce editor

wp-style-dropdown.php

<?php

/*
 * Custom styles for tiny mce
 * HT: http://alisothegeek.com/2011/05/tinymce-styles-dropdown-wordpress-visual-editor/
 */

add_filter( 'mce_buttons_2', 'my_mce_buttons_2' );
function my_mce_buttons_2( $buttons ) {
    array_unshift( $buttons, 'styleselect' );
    return $buttons;
}

add_filter( 'tiny_mce_before_init', 'my_mce_before_init' );
function my_mce_before_init( $settings ) {

    $style_formats = array(
    	array(
    		'title' => 'Button',
    		'selector' => 'a',
    		'classes' => 'button'
    	),
	array(
		'title' => 'Intro paragraph',
		'selector' => 'p',
		'classes' => 'intro'
	),
	array(
		'title' => 'Callout',
		'selector' => 'p',
		'classes' => 'callout'
	)
    );

    $settings[ 'style_formats' ] = json_encode( $style_formats );

    return $settings;

}

?>