Some still use the old faithful notepad or vi for php development while others jump onto the latest and greatest ide any chance they get. This list for all the current decent ides out there.
I like Visual Studio and so I gave VS.PHP a try but it crashed on me continously after install. It could be because I installed Visual Studio 2010 Express first and VS required the standard edition (or else it installs its own visual studio shell). During the few times I could get into the software, it was fast and the syntax highlighting looked decent. Wasn't able to try debugging with XDebug on it but would be nice to be able to debug php in a visual studio environment.
Current favorite, it's free, fast, and did I mention it's free?
Under the options menu, you can even set the ide to open .html as if they're php to get php highlighting in your html files (which is nice if you have a lot of php in your html).