Cake PHP
CakePHP might just be the most popular PHP framework around right now. Also uses the MVC framework. CakePHP is a little heavier than CodeIgniter and Kohana but has it has its own advantages.
Vork
Vork is intuitive & easy to use and does not have the overhead or performance-penalty typical in PHP frameworks
Symfony
Symfony is a web application framework for PHP5 projects.
It aims to speed up the creation and maintenance of web applications, and to replace the repetitive coding tasks by power, control and pleasure.
Zend Framework
Extending the art & spirit of PHP, Zend Framework is based on simplicity, object-oriented best practices, corporate friendly licensing, and a rigorously tested agile codebase.
Fat Free
Condensed in a single 55KB file, the framework's simple domain-specific language gives you access to Fat-Free's all-purpose template engine, flexible cache, automatic spam protection, integrated unit testing tools, and code profiler.
Akelos
The Akelos PHP Framework is a web application development platform based on the MVC (Model View Controller) design pattern similar to Ruby on Rails.
Flourish
Flourish is a PHP unframework — a general-purpose, object-oriented library. It has a modular architecture, meaning it isn't strictly MVC.
Konstrukt
Konstrukt is a very light weight PHP framework with the following key aspects:
•   Controllers are resources
•   URI-to-controller-mapping gives your application a logical structure
•   Routing based on logic rather than rules

CodeIgniter
CodeIgniter is a powerful, high-performance, open-source PHP framework that helps you author PHP applications rapidly
LightVC
LightVC is comparable to, although unlike, CakePHP, Code Igniter, symfony, Solar, and Zend Framework to name a few
Adroit
Adroit is a lightweight PHP 5 MVC framework that is geared towards helping you develop faster. The main motivation behind Adroit is to keep it simple, but provide useful features that developers want.