One of the most important decisions a PHP programmer makes is the choice of MVC Framework. There are several very good ones around and the choice is usually a personal preference based both on a technical and subjective decision.
Frameworks allow a programmer to strongly start and rapidly develop a project. If you don’t use one, my advice is to adopt one as soon as possible.
This year we have seen a clear leader in Yii. Yii is fairly easy to learn, well documented and has good all round features that make it good for a wide range of projects, from small to large.