I don't think there's a plugin available just for that, but you can easily accomplish it with a few minor edits.

First, edit you includes/modules/pages/product_info/main_template_vars.php and replace this
Code:
    $sql = "select p.products_id, pd.products_name,
                  pd.products_description, p.products_model,
                  p.products_quantity, p.products_image,
                  pd.products_url, p.products_price,
                  p.products_tax_class_id, p.products_date_added,
                  p.products_date_available, p.manufacturers_id, p.products_quantity,
                  p.products_weight, p.products_priced_by_attribute, p.product_is_free,
                  p.products_qty_box_status,
                  p.products_quantity_order_max,
                  p.products_discount_type, p.products_discount_type_from, p.products_sort_order, p.products_price_sorter
           from   " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_DESCRIPTION . " pd
           where  p.products_status = '1'
           and    p.products_id = '" . (int)$_GET['products_id'] . "'
           and    pd.products_id = p.products_id
           and    pd.language_id = '" . (int)$_SESSION['languages_id'] . "'";
with
Code:
$sql = "select p.products_id, pd.products_name,
                  pd.products_description, p.products_model,
                  p.products_quantity, p.products_image,
                  pd.products_url, p.products_price,
                  p.products_tax_class_id, p.products_date_added,
                  p.products_date_available, p.manufacturers_id, p.products_quantity,
                  p.products_weight, p.products_priced_by_attribute, p.product_is_free,
                  p.products_qty_box_status,
                  p.products_quantity_order_max,
                  p.products_discount_type, p.products_discount_type_from, p.products_sort_order, p.products_price_sorter, pd.products_viewed
           from   " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_DESCRIPTION . " pd
           where  p.products_status = '1'
           and    p.products_id = '" . (int)$_GET['products_id'] . "'
           and    pd.products_id = p.products_id
           and    pd.language_id = '" . (int)$_SESSION['languages_id'] . "'";
Then, add
Code:
$products_viewed = $product_info->fields['products_viewed'];
somewhere between lines 99 and 133, for example right after
Code:
$products_url = $product_info->fields['products_url'];
Next, edit your includes/templates/YOUR_TEMPLATE/templates/tpl_product_info_display.php and add the following line where you want to display the counter:
Code:
<?php echo 'This product was viewed ' . $products_viewed . ' times'; ?>
The language is obviously hard-coded in this case, but you can easily change it into a definition if you want...