Symfony Documentation
Symfony is arguably the best PHP framework out there at the moment. It has a huge amount of functionailty and a large and active community.
To help you get started, the creators have provided a wide variety of resources.
The documentation for the latest version, 1.4 is here: http://www.symfony-project.org/doc/1_4/
The Getting Started tutorial might be your first port of call: http://www.symfony-project.org/getting-started/1_4/en/
In older versions of Symfony, there are some excellent step-by-step tutorials on how to build a complete web application:
Symfony does have a steep learning curve, but stick with it. It's worth it!