Notepad++ hands down. It's simple, fast and gets the job done. The syntax highlighting is perfect and it even has heredoc support.
Someone said that Notepad++ has a list of PHP functions built-in, how do you take advantage of this?
I tried NetBeans but it seems to over complicate what I need to do. I just want to be able to open up a PHP file or make a new one and do my work. The project thing is cool, but I hate constricting my files into one folder. I'm use to working in a vBulletin environment, since that's what my web site largely consists of, so having the entire forums directory as a project doesn't work out. It has some nice features, no doubt, but it's just not for me.