Add a selectable "Styles" menu to TinyMCE, so users can apply certain classes without needed to dig into the markup or use shortcodes.

gistfile1.php

<?php
/** 
 * Add "Styles" drop-down to TinyMCE
 *
 * @since 1.0.0
 * @link http://wp.tutsplus.com/tutorials/theme-development/adding-custom-styles-in-wordpress-tinymce-editor/
 * @param array $buttons
 * @return array
 */
function ja_mce_editor_buttons( $buttons ) {
	array_unshift( $buttons, 'styleselect' );
	return $buttons;
}
add_filter( 'mce_buttons_2', 'ja_mce_editor_buttons' );

/** 
 * Add styles/classes to the TinyMCE "Styles" drop-down 
 *
 * @since 1.0.0
 * @link http://wp.tutsplus.com/tutorials/theme-development/adding-custom-styles-in-wordpress-tinymce-editor/
 * @param array $settings
 * @return array
 */
function ja_mce_before_init( $settings ) {

	$style_formats = array(
		array(
			'title'    => 'Paragraph Large',
			'selector' => 'p',
			'classes'  => 'large',
		),
	);
	$settings['style_formats'] = json_encode( $style_formats );
	return $settings;
}
add_filter( 'tiny_mce_before_init', 'ja_mce_before_init' );