The first and most obvious place to start, is that which is at the centre of the universe for a PHP developer, his IDE of choice and at present, that honour goes to PhpStorm.
Back in the day when I first started out coding in PHP I used PHPEdit. It was free and built around speed and productivity. I still miss their drop marks feature and surprised other IDEs have not incorporated this into their environments. Once it became commercial, I moved onto something else unmemorable, before adopting Zend Studio 5 and 5.5. Good days. I then persisted with Zend Studio 6 for Eclipse but refused to shell out for 7 and switched to Netbeans after hearing good things. I was happy for months until I started having performance issues. After failing to resolve this annoyance I finally moved onto PhpStorm and haven’t looked back.