Taco HTML Edit is one of many quality text editors for Mac. This one has a beautiful interface and several functional features: syntax highlighting, code tidying, syntax check, and a hotkey for previewing in a browser.
This app could easily be renamed "Taco PHP Edit" because it is equally functional with PHP as with HTML. It can even do browser previews of PHP code if you specify the location of your PHP binary in the Preferences.
This is a great editor for any web designer, programmer, or student.