Singleton style plugin reference

Init

if ( ! defined( 'ABSPATH' ) ) exit;

add_action( 'plugins_loaded', array( 'Plugin_Class_Name', 'get_instance' ) );

class Plugin_Class_Name {

	private static $instance = null;

	public static function get_instance() {
		if ( ! isset( self::$instance ) )
			self::$instance = new self;

		return self::$instance;
	}

	private function __construct() {
		// Register hooks and shit here
	}

}