Exemplo de Integração do módulo de Drupal http://drupal.org/project/pagseguro, para integrar ao PagSeguro puramente, sem estar dentro de um ecommerce

gistfile1.php

pagseguro_library_load();
  $PagSeguroAPI = new PagSeguroAPI();

  $payment_request = $PagSeguroAPI->createPaymentRequestObject();
  $payment_request->setCurrency("BRL");
  $payment_request->setReference($order_reference);
  $payment_request->setSender($customer_name, $order->mail);
  $payment_request->setRedirectUrl("http://example.com/pagseguro/return");

  // Shipping rate is handled by Drupal
  $CODIGO_SEDEX = PagSeguroShippingType::getCodeByType('NOT_SPECIFIED');
  $payment_request->setShippingType($CODIGO_SEDEX);
  $payment_request->setShippingAddress(
      $postal_code, $customer_street, NULL, NULL, $customer_district
      , $customer_city, $customer_region, 'BRA'
  );

  foreach ($order->commerce_line_items[LANGUAGE_NONE] as $key => $value) {
    $line_item_ids[] = $value['line_item_id'];
  }

  $line_items = commerce_line_item_load_multiple($line_item_ids);

  if ($settings['individual_items']) {
    $index = 1;
    foreach ($line_items as $line_item) {
      $line_item_wrapper = entity_metadata_wrapper('commerce_line_item', $line_item);
      if ($line_item->type == 'shipping') {
        $line_item_id = $line_item_wrapper->commerce_shipping_service->value();
        $product_title = commerce_line_item_title($line_item); // TRUC specific
      }
      else {
        $line_item_id = $line_item_wrapper->commerce_product->product_id->value();
        if ($line_item->type == 'moldura_galeria') {
          $product_title = $line_item_wrapper->field_imagem_da_galeria->title->value() . ' - ' . $line_item_wrapper->commerce_product->title->value(); // TRUC specific
        }
        else {
          $product_title = commerce_line_item_title($line_item); // TRUC specific
        }
      }
      $unit_price = commerce_price_wrapper_value($line_item_wrapper, 'commerce_unit_price', TRUE);

      if (!empty($unit_price['amount'])) {
        $payment_request->addItem(
            $line_item_id
            , $product_title
            , (int) $line_item->quantity
            // PagSeguro uses a number format different than Drupal, that's why the
            // amount is divided by 100
            , number_format(($unit_price['amount'] / 100), 2)
        );
      }

      $index++;
    }
    unset($index);
  }
  else {
    // Send everything as a single item.
    $payment_request->addItem(
        $order->order_number
        , t('Order @order_id', array('@order_id' => $order->order_number))
        , 1
        , number_format(($order_wrapper->commerce_order_total->amount->value() / 100), 2)
    );
  }

  $request_url = $PagSeguroAPI->registerPaymentRequest($payment_request);

  drupal_goto($request_url);