display all registered meta boxes

All the meta boxes are kept in a multidimensional array, called $wp_meta_boxes. It will display all of the meta boxes registered for a specific screen and a specific context.

Use the following code:

function get_meta_boxes( $screen = null, $context="advanced" ) {
    global $wp_meta_boxes;

    if ( empty( $screen ) )
        $screen = get_current_screen();
    elseif ( is_string( $screen ) )
        $screen = convert_to_screen( $screen );

    $page = $screen->id;

    return $wp_meta_boxes[$page][$context];          
}

Now, if you want to get an array that contains all of the meta boxes that are of “normal” priority, you have to use the following code:

$dashboard_boxes = get_meta_boxes( 'dashboard', 'normal' );