As you might know, I am a big fan of GraphViz. I’ve used numerous times for visualizing different parts of the project code and dependencies (see here and here for example).
Today I came across a way to visualize PHP objects (not just classes) – object-graph library by Sebastian Bergmann, and I think it’s pretty cool. If you are working on top of a PHP framework like CakePHP and Laravel, I suspect your object diagrams will get quite huge, but for more modular applications and libraries it should do the job just fine.