Wow, I'm suprised Dreamweaver got this many votes, even if the topic is almost 4 years old. Didn't even realize they still make it. From my experience you're better off with Vim (which I do use for quick edits of config files but find lacking as an IDE).
That said, the single feature I find most useful in an IDE is code completion. I suffer from what we Dutch refer to as "geheugen als een goudvis", which compares one's short term memory to the proposed 3 seconds of retention a goldfish possesses. Unfortunately this is also the feature that provides the biggest challenge to IDE developers in terms of performance when library size approaches he gigabyte. I've tried quite a few. PHPStorm seems perform best right now. ZSfE was awesome featurewise, I might give it another try to see if it performs better now