I agree with this: Netbeans is a good IDE for Symfony development. I think this is especially true if you, like me, also develop with JVM languages. This last year I was doing some Java/Swing and Groovy projects, so I started using NetBeans again. It has a plugin for doing Symfony work - very handy.

(Off topic, the more I work with Groovy, the more I think this is the perfect language for PHP developers who want to learn a JVM language.)