These are the five most important tools for any php developer:

1) Crimson editor:
This program is very small in size and server as a good replacement for Notepad and can be used as an editor in programming languages like C/C++, HTML and Java etc.

2) VS.php:
This provides an integrated development environment based on Visual studio. Using this tool you can design, develop, debug, and deploy php applications within the Visual Studio IDE. This editor offers code completion for all php functions.

3) ez_sql/ez_results - MySQL wrapper library:
This an SQL library that features disk caching, has excellent debug functions, allows the use of much smaller ezSQL functions, it can return results as Objects, Associate Arrays or Numeric Arrays and also works with Smarty templating language.

4) Smarty Template Engine:
This is an excellent template engine for php and supports the facility of separation of application code from the presentation.

5) MySQL GUI Bundle:
This suite of GUI tools includes MySQL Administrator, MySQL Query Browser, MySQL Migration Toolkit and MySQL Workbench.

With mostly all these plugins available for free, I think that they should be downloaded by every php programmer.

via: whenpenguinsattack