PHP is exploding in popularity right now, especially among web application developers.  I've been asked several times which PHP editor is the best, and I always give out the same answer:

Zend Studio

Zend actually created PHP as well as the engine that all PHP applications run on, so they know exactly what they're doing.  The Zend Studio PHP editing application is the only Integrated Development Environment that includes all components necessary for complete PHP development.

If you don't know what any of that stuff means, don't worry.  Just understand this -- Zend will speed up your PHP development cycle so that you can earn more money - that's all you need to know...