The very cool Komodo IDE has API support for Drupal. Very nice code completion/documentation for Drupal API functions.
This was apparently the result of a request from the Drupal community. Nice.
I recommend the Komodo IDE for all LAMP/Web development. It's by far the most mature of the IDEs available for PHP/Perl/HTML/Javascript/CSS work. The only drawback is that it's not free. It will run you about $300, but if you program for a living, it pays for itself very quickly.
