Cal Evans has put together a list of five things he thinks that every PHP developer out there should be equipped with in their development.
Over the past nine years of having fun with PHP, began to see that there are five categories of tools that I rely on more than any others. Sure, I've got a code beautifier, a standards checker, and a hand full of hand-written scripts I use for various things to make life easier. However when it comes down to it, there are five that I rely on every day. So here they are in acceding order of importance. Let me know, what are your five? (let's not start a meme or anything though, ok?)
His list of five is: a unit testing tool, a debugger, an ERD tool (Entity Relationship Diagram), a version control system and, finally, a framework (pick a framework, any framework).