Jeez Tech has a new post with a great (and long) list of PHP scripts to connect your application to any number of popular APIs out there.
Do you want to use an API but you are too lazy to write your own code to handle the requests? If you code in PHP as I do, then you will definitely need these classes. By using the classes listed here you will be able of using a great number of web services with an easy and documented way.
They link to libraries to work with the APIs for Alexa, Babelfish, Bing, eBay, Facebooks, Flickr, Linkedin, MSN, Twitter, Skype and Yahoo. They also mention PEAR and the role it plays in the foundation of many web service connections.