I use Eclipse (
http://eclipse.org )
Since using it, I haven't used anything else. I'm not sure how many plugins it has, but I've been using it for java, php, html, css and ruby / rails. It has code completion / method helpers for java, php and html ( there's probably others ). Have been using it with its subversion plugin to manage projects at work on a couple of windows boxes plus use it on my laptop running linux. Since it's java based, it might not be the fastest gui in the world but I just find it invaluable in what it supports and the platforms it runs on.
Plus, it's free.
*shrug*