Another editor, not PHP specific, is Activestate Komodo. http://www.activestate.com/Products/Komodo/
Ive used it for quite a while and its pretty decent. One warning, it does chew up a bit of resources, so if you have a slow computer forget running it.
They actually have 2 pricing models for it. $29.95 for "educational" use. If your not working for a company, and if you are, its $295.00. The major selling points for me on it were a built in regex builder. You can create regular expressions very easily and even test them. And the biggest selling point was that it has background syntax checking. You just tell it where PHP is installed and itll run your code as you write it. If theres an error in your code you get little squigglies similar to how MS Word tells you that you misspelled a word. Even gives you the error message when you click on the code thats wrong. I love it for catching things when I forget a semicolon or i forget to escape a quote. It also has support for perl, tcl, python and a bunch of other languages. Also has CVS integration.
Nice editor, but like I said, it is pretty resource hungry. But on the whole, real nice IDE.