Sitepoint, widely known for quality in content and tutorials, has a new post on its Site Marketing blog today dealing with tracking a site's Google ranking with the help of the Google API and the PEAR SOAP package.
Bernard Peh, the author, sets up what the Google API is and includes the way to grab your own API key (your pass into the powerful Google backend). The other two requirements for the project are the PEAR SOAP package and an install of at least PHP 4 or higher.
There's a list of input parameters for the functionality, with each described for what it does, and pley of code to help you integrate them into the API call. They give the example of the class grabbing the needed info (via SOAP), parsing out your URL from those results, and a simple form to make checking different URLs all the simpler.