With PHPEclipse there is a decent plugin for PHP within Eclipse available, although it isn’t yet as feature rich as Eclipse for Java development it is quite usable. In combination with the Subversion plugin development becomes even easier.
Note that there is also an official PHP-IDE from Eclipse which is developed together with Zend. This is however in a early development state and I haven’t had time to take a closer look at it. In the long term this is probably the solution to go with.
All in all I am quite happy with the development environment.