* Syntax hilighting (any text editor can have this)
* Find Resource by starting to type the filename
* Follow function calls
* integrated debugger
I used visual studio a long time ago, now any ide without a debugger seems quaint.
I use NetBeans and NuSphere (PHP IDE) both are OK. The NuSphere PHP/debug plugin is ace. You can pause, edit variables, run random commands, move execution to a different point, all sorts of cool stuff.
Also love the chrome JS debugger, it's a bit verbose for my liking, maybe that's JS having a lot of crap bundled in objects all visible by default.