I started an XML service that returns geographic data when you provide a valid address in the URL. The type of data that is returned is:
city
county
state
zipcode
areacode(s)
latitude
longitude
elevation
timezone

Here's a sample:
http://www.digital-seven.net/geodata/?address1=19355%20Sherman%20Way%20Reseda,%20CA

If you would like to learn how to use this in your PHP scripts, you can find additional information here:
http://www.digital-seven.net/index.php?option=com_content&task=view&id=69&Itemid=45

Enjoy!