I use Eclipse PDT for my own development because it's been the stalwart free-and-open-source PHP development platform. There are some other options now, but I've gotten used to it and I appreciate it's independent nature (just maintained by a dedicated team of enthusiasts) as opposed to a large company.
What I'm looking forward to the most is the future improved support for frameworks like Symfony, Laravel, and things like Blade templates and Facades (used by Laravel).