If you're on Windows, check out WebMatrix 2.
Microsoft actually pumped out a decent IDE with code completion for web development.
Just stay away from their razer syntax or whatever the hell they made up...
They support PHP and Javascript which is what really matters. Also, they have built in tools for minifying your CSS and JS files. (If you want to use sass or less that's supported too)
Otherwise, for quick edits, notepad++