Shortcodes

/* Add code, like iframe, to post via custom field shortcode
[field name=custom-field-name]
put code in custom field w/ above name
http://www.vividvisions.com/2009/02/11/wordpress-add-iframes-to-your-post/
*/
function field_func($atts) {
   global $post;
   $name = $atts['name'];
   if (empty($name)) return;

   return get_post_meta($post->ID, $name, true);
}

add_shortcode('field', 'field_func');