Objective Development have created a freeware extension bundle for Apple's XCode which adds functionality for making PHP development more comfortable. Currently implemented are a PHP system function lookup (including parameter hints) and a shortcut for looking up the PHP online help for a given function.
[robg adds: This plug-in worked fine when I tested it on Xcode 2.1, and could be a timesaver if you do PHP development in Xcode.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050730061123413