If you want your wordpress login and registration pages according to your wordpress theme and also some customizable setting example:email,security , then Theme my login wordpress plugin is useful for you. It replaces the wp-login.php file by using a page template from your theme and also includes a widget for sidebar login.
To customize login and registration page in wordpress
1. Download Theme My Login wordpress Plugin from this link.
2. Unzip and upload it to your WordPress wp-content/plugins directory.