If you want a full featured editor, you might try XCode. Don't know if it supports php (auto-complete, etc). It's free.
Let me get this straight. You're in the
web design and development area, the OP asks for
PHP, and you say "Xcode. I don't know if it supports PHP [...]". Wtf is wrong with you, people?
Yes, Xcode does support PHP, if you want to download a 1GB
*.dmg and install a 4GB application for the most minimalist PHP editor out there.
I think it's all about your needs. I used CoDA, but I only develop offline, so no need for its advanced features, and the interface is too bloated for my taste. I used Dreamweaver but I've got sick of its bugs, so I switched over to TextMate, which, apart from helping me A LOT in debugging, is also nice and user-friendly. So do some savings, and go buy TextMate.
So to put it simple: CoDA if you use its features and need them enough in order to justify the price, Dreamweaver if you want the most powerful tool (includes Spry -- its own AJAX framework -- powerful WYSIWYG, Live View, and, if you're using the Code View, the syntax guidelines are an awesome asset!), TextMate/TextWrangler if you simply want a powerful Code Editor (with the latter being free).