A look at PHPeclipse
In another post ( IBM is taking PHP (and Drupal) very seriously ), I mention a series of articles IBM is writing in the context of using Drupal as a web application framework.
In Part 6: Building a custom module in Drupal it is mentioned (and you can see from the graphics) that they are using PHPeclipse in their IDE.
Which I have done. Will report as concretely used in a project.