An example WordPress custom loop to show all custom post types.

custom_loop.php

<?php
// Set-up the loop with all custom post types
$post_types = array( 'post', 'link', 'snippet', 'doodle' );
$paged = ( get_query_var( 'paged' ) ) ? get_query_var( 'paged' ) : 1;
$args = array(
	'post_type' 		=> $post_types,
	'paged' 			=> $paged,
	'posts_per_page'	=> 10
	);
query_posts( $args );