http://www.symfony-project.com/

an open-source PHP web framework

http://www.cakephp.org/

A rapid development framework for PHP that provides an extensible architecture for developing, maintaining, and deploying applications.

http://www.ezluk.org/

http://fuelphp.com/

FuelPHP is a simple, flexible, community driven PHP 5.3 web framework based on the best ideas of other frameworks with a fresh start.