Not many useful PHP books have been published recently (or I haven’t yet discovered them), so I really want to recommend “Modern PHP” by Josh Lockart, another quality product by O’Reilly.
Having only 270 pages, it’s easy and quick to read, and includes a lot of best practices, tips and state-of-the-art tools for writing cool PHP applications. Some topics are covered a bit briefly like e.g. Testing, but the book points you towards the right direction and gives you useful references to read further, if you are interested.
The experienced PHP developer should actually be familiar with most of the topics, so you would probably not learn too much new stuff. Still it gives the good feeling of confirming that you are somewhat up-to-date 🙂