Mage::getResourceSingleton('catalog/product')
  ->getAttributeRawValue($productId, 'attribute_code', Mage::app()->getStore());

Mage::getResourceSingleton('catalog/product')
  ->getAttributeRawValue($productId, 'url_key', Mage::app()->getStore());

$product_collection = Mage::getModel('catalog/product')->getCollection()
    ->addAttributeToFilter('entity_id', 16)
    ->addUrlRewrite();
$product_collection_url = $product_collection->getFirstItem()->getProductUrl();

$_item = Mage::getModel('catalog/product')->getCollection()
    ->addAttributeToSelect('product_url')
    ->addAttributeToFilter('entity_id', $productId)
    ->addUrlRewrite()
    ->load();

foreach($_item as $product){
    echo $product->getProductUrl();
}

// returns string "http://www.your-domain.com/[category]/[product_url]"

Mage::getResourceSingleton('catalog/product')
      ->getAttributeRawValue($productId, 'url_key', Mage::app()->getStore());

// returns string "product-url-like-this"

$productUrl = Mage::getResourceModel('core/url_rewrite')
    ->getRequestPathByIdPath('product/' . $productId, $storeId);
    // returns string "product-url.html"