The Zend Framework is an object-oriented framework which is focusing on web 2.0 applications. It contains a lot of APIs to webservices like Google, Amazon, Yahoo!, Flickr.
PHP CSV Utilities or PCU, is a small, open source PHP library to simplify working with CSV files.
This project provides a set of classes, which allow you to write to and read from different file formats, like Excel 2007, PDF, HTML, … This project is built around Microsoft’s OpenXML standard and PHP.
MC_Google_Visualization provides simple support for integrating Google Visualization charts and graphs with your own internal database. It includes a complete parser for the Google Visualization Query Language, giving you the same ease of pivoting and formatting data from your database as is currently possible with Google Spreadsheets.
pChart is a PHP class oriented framework designed to create aliased charts.
FirePHP enables you to log to your Firebug Console using a simple PHP method call.
The SimpleTest PHP unit tester is a PHP unit test and web test framework. It has support for SSL, forms, frames, proxies and basic authentication.
If you know any more good PHP libraries and tools, just leave a comment.