Favorite PHP Frameworks

[bjk2007]

I just started a major application development project and decided to start out off a favorite. I picked one and I've really liked working with it so far. I decided that it would be good to ask the question:
What's your favorite PHP framework and why?

P.S.-I got the list for the poll by combining the list in Wikipedia (http://en.wikipedia.org/wiki/PHP_frameworks) with a PHPit Top Ten list (http://www.phpit.net/article/ten-different-php-frameworks/).

[bjk2007]

My favorite PHP framework is Code Igniter.

A friend recommended code igniter to me after he discovered it. For him to really get excited over a framework takes a lot because he's the type of person who would rather build it better himself from scratch. I downloaded it and tried it out and it's been working out great. The only problem I've had with it is a few issues with the email library.