Add additional image sizes to the WordPress media upload/insert interface

functions.php

<?php
/**
 * Add additional image sizes to the WordPress media upload/insert interface
 * 
 * @author Daniel Roizer
 * @link http://goo.gl/0tKD0
 */
function iweb_additional_image_sizes( $sizes ) {
	$additional_image_sizes = array(
		'banner' => 'Banner'
	);
	
	return array_merge( $sizes, $additional_image_sizes );
}
add_filter( 'image_size_names_choose', 'iweb_additional_image_sizes' );