Probably depends upon what you are developing. For template development, dreamweaver seems to get a lot of support around here.
For php/component/module development, where the emphasis is on php coding, I suspect that things will be quite different.
I hang around in the php circles, so my answer is biased from that point of view. I do little to no template development and tend to make small changes when appropriate to my templates.
My favorite is PHP 2005 available from
http://www.mpsoftware.dk/ . I also REALLY like the products available from Zend, but they are not open source and kind of pricey.