Going along to one of the PHP events around the world is a great way to meet up with your peers and share ideas, solutions, and learn new things. These conferences are usually a mix between general discussion between attendees, a sponsor expo where you can look at companies involved in the PHP arena, and also tutorials where you listen to lectures from luminaries in various fields about new developments in PHP.
If you're only going to go to one conference, I'd recommend you make it O'Reilly's Open Source Convention: it covers a variety of programming languages and platforms, but PHP always puts in a good show there. If not that, then consider the International PHP Conference, which tends to cover more detailed topics due to its specific focus on PHP.
If you've never been to a big conference before, here are some hints: take a spiral-bound A5 notepad with you for writing, a selection of cheap pens (you'll lose most of them, but should get freebies to replace them while at the conference!), some small snacks to keep you going between meals, and, of course, a WiFi-compatible laptop. Apple laptops are becoming increasingly prevalent, but anything that supports 802.11b/g is good.