A small plugin to show all saved custom fields names and values. Useful in debugging.

scfd.php

<?php 
	// Plugin Name: Show Custom Fields Data
	// Description: This plugin adds a metabox and shows all the custom fields names and data
	// Author: Zenger
	// Author URI: http://github.com/Zenger/
	// Version: 1.0
	
	function scfd_add_meta_box()
	{
		foreach (get_post_types() as $post_type)
		{
			add_meta_box( "scfd", "Custom Fields Data", "scfd_show_scfd_data", $post_type, "normal", "low", $post_type );
		}
	}
	add_action('add_meta_boxes', 'scfd_add_meta_box');

	function scfd_show_scfd_data($post , $args = null)
	{
		echo "<pre>".print_r(get_post_meta($post->ID) , true)."</pre>";
	}