Drupal 7: create node_types select options, form api

gistfile1.php

<?php 
  // node_types select options
  $types = node_type_get_types();
  foreach($types as $node_type) {
    $options[$node_type->type] = $node_type->name;
  }
  $form['onpay']['onpay_node_types'] = array(
    '#type' => 'select',
    '#title' => t('Node types'),
    '#options' => $options,
    '#multiple' => TRUE,
    '#default_value' => variable_get('onpay_node_types', array());
  );
?>