I continue to be gassed by how easy it is to manipulate XML with PHP5. Here's an example of how to get current weather data onto your page using an XML feed from the U.S. National Weather Service.
First, go to NOAA and find the feed closest to you. Start here:
Get the URL of the XML feed, not the RSS feed. The XML feed provides finegrained information.
Here I grab the data for Daniel Field, an airport in Augusta, Ga.
$url = 'http://www.nws.noaa.gov/data/current_obs/KDNL.xml';
$xml = simplexml_load_file($url);
You can read the XML itself to figure out the potential names of items of interest, or you can print_r() the $xml variable. Either way, it's not hard to figure out the name of what you want to display. In my case, all I wanted was a brief statement of current conditions, the temperature (F and C), and the humidity. There's a lot of other information in the file, as well as alternative presentations of the basic data.
Then do something like this:
echo '<b>Augusta weather: </b><br />';
echo $xml->weather, '<br />';
echo $xml->temperature_string, '<br />';
echo $xml->relative_humidity, '% humidity <br />';
It's that simple.
Now, every time your page is displayed, it has to hit the NOAA server to get the latest information. You may want to retrieve the XML file, cache it, and have simplexml_load_file() refer to the cached version instead of directly hitting the URL as I did in this example.