Gweather is a project mainly written in PHP, it's free.
PHP class that retrieves weather information from Google
example:
<?php require_once 'gweather.class.php';
$wt = new gWeather;
$data_weather = $wt->getData(array('cidade' => 'campo grande', 'pais' => 'brasil'));
echo $wt->getHtmlExample();
?>