Class for creating custom post types, taxonomies and meta boxes via: http://new2wp.com/pro/wordpress-custom-post-types-object-oriented-series2

cpt-class-create.php

<?php
// Create a post type class for site posts
// To use as a bookmarking post type for sites you want to save/share.
class TypeSites {
    public $meta_fields = array( 'title', 'description', 'siteurl', 'category', 'post_tags' );

	public function TypeSites() {

        $siteArgs = array(
			'labels' => array(
                'name' => __( 'Sites', 'post type general name' ),
                'singular_name' => __( 'Site', 'post type singular name' ),
                'add_new' => __( 'Add New', 'site' ),
                'add_new_item' => __( 'Add New Site' ),
                'edit_item' => __( 'Edit Site' ),
                'new_item' => __( 'New Site' ),
                'view_item' => __( 'View Site' ),
                'search_items' => __( 'Search Sites' ),
                'not_found' =>  __( 'No sites found in search' ),
                'not_found_in_trash' => __( 'No sites found in Trash' ),
			),
			'public' => true, 'show_ui' => true,
			'_builtin' => false,
			'capability_type' => 'post',
			'hierarchical' => false,
			'rewrite' => array('slug' => 'site'), // Permalinks. Fixes a 404 bug
			'query_var' => 'site',
			'taxonomies' =>  array('category', 'post_tag'), // Add tags and categories taxonomies
			'supports' => array('title','editor','author','comments')
        );

        register_post_type( 'site', $siteArgs );	

	}

} // end of TypeSites{} class

/********************** Add Methods to TypeSites Class *************************/
// Create the columns and heading title text
public function site_edit_columns($columns) {
       $columns = array(
		'cb' 		=> '<input type="checkbox" />',
		'title' 		=> 'Site Title',
		'url'	 	=> 'URL',
		'category'	=> 'Category',
		'post_tags' => 'Tags',
		'siteurl' 	=> 'Screenshot',
       );
       return $columns;
   }
// switching cases based on which $column we show the content of it
   public function site_custom_columns($column) {
	global $post;
       switch ($column) {
           case "title" : the_title();
               break;
           case "url" : $m = $this->mshot(150); echo '<a href="'.$m[0].'" target="_blank">'.$m[0].'</a>';
			break;
           case "category" : the_category();
			break;
           case "post_tags" : the_tags('',', ');
               break;
           case "siteurl" : $m = $this->mshot(150); echo $m[1];
			break;
       }
   }
// Template redirect for custom templates
   public function template_redirect() {
       global $wp_query;
       if ($wp_query->query_vars['post_type'] == 'site') {
           include(TEMPLATEPATH . '/single-site.php'); // a custom single-slug.php template
           die();
       } else {
		$wp_query->is_404 = true;
	}
   }

/****************************** Insert posts function ******************************/
// For inserting posts
   public function wp_insert_post($post_id, $post = null) {
       if ($post->post_type == "site") {
           foreach ($this->meta_fields as $key) {
               $value = @$_POST[$key];
               if (empty($value)) {
                   delete_post_meta($post_id, $key);
                   continue;
               }
               if (!is_array($value)) {
                   if (!update_post_meta($post_id, $key, $value)) {
                       add_post_meta($post_id, $key, $value);
                   }
               } else {
                   delete_post_meta($post_id, $key);
                   foreach ($value as $entry) add_post_meta($post_id, $key, $entry);
               }
           }
       }
   }

/********************************* Add Meta Box Functions **********************************/
// Add meta box
function admin_init() {
	add_meta_box("siteS-meta", "Site", array(&$this, "meta_options"), "site", "side", "high");
}

// Admin post meta contents
public function meta_options() {
	global $post, $url;
	$custom = get_post_custom($post->ID);
	$url = $custom["siteurl"][0];
	$myurl = trailingslashit( get_post_meta( $post->ID, 'siteurl', true ) );
	if ( $myurl != '' ) {
		if ( preg_match( "/http(s?):\/\//", $myurl )) {
			$siteurl = get_post_meta( $post->ID, 'siteurl', true );
			$mshoturl = 'http://s.wordpress.com/mshots/v1/' . urlencode( $myurl );
		} else {
			$siteurl = 'http://' . get_post_meta( $post->ID, 'siteurl', true );
			$mshoturl = 'http://s.wordpress.com/mshots/v1/' . urlencode( 'http://' . $myurl );
		}
		$imgsrc  = '<img src="' . $mshoturl . '?w=250" alt="' . $title . '" title="' . $title . '" />';
	} ?>
	<p><label>Clean Url: <input id="siteurl" size="26" name="siteurl" value="<?php echo $url; ?>" /></label></p>
	<p><label>Mshot Url: <input id="mshoturl" size="26" name="mshoturl" value="<?php echo $mshoturl; ?>" /></label></p>
	<p><?php echo '<a href="'.$siteurl.'">'.$imgsrc.'</a>'; ?></p>
<?php
} // end meta options

public function mshot($mshotsize) {
	global $post, $url;
	$imgWidth = $mshotsize;
	$myurl = get_post_meta($post->ID, 'siteurl', true);
	if ( $myurl != '' ) {
		if ( preg_match( "/http(s?):\/\//", $myurl )) {
			$siteurl = get_post_meta( $post->ID, 'siteurl', true );
			$mshoturl = 'http://s.wordpress.com/mshots/v1/' . urlencode( $myurl );
		} else {
			$siteurl = 'http://' . get_post_meta( $post->ID, 'siteurl', true );
			$mshoturl = 'http://s.wordpress.com/mshots/v1/' . urlencode('http://'.$myurl );
		}
	}
	$mshotimg = '<img src="'.$mshoturl.'?w='.$imgWidth.'" alt="'.get_the_title().'" title="'.get_the_title().'" />';

	return array( $siteurl, $mshotimg );
}

/******************************* Initialize Class functions *****************************/
      add_action( 'admin_init', array(&$this, 'admin_init') ); // this must be first
      add_action( 'template_redirect', array(&$this, 'template_redirect') );
      add_action( 'wp_insert_post', array(&$this, 'wp_insert_post'), 10, 2 );

// add custom columns
add_filter( 'manage_posts_custom_column', array( &$this, 'site_custom_columns' ));
add_action( 'manage_edit-site_columns', array ( &$this, 'site_edit_columns' )); // manage_edit-{post_type}_columns used for custom post types

/* Initialize Post Types */
add_action('init', 'pTypesInit');
function pTypesInit() {
    global $sites;
    $sites = new TypeSites();
}
?>