Since any basic text editor can write HTML, CSS, and various scripting languages, I like to let my students know which I recommend and why.
I have two favorites. Both are free. Both use color coding and indentation to make reading and troubleshooting easier. Both provide line numbering. One is for Mac and one is for Windows.
For the Mac, I like TextWrangler. TextWrangler is a “lite” version of BBEdit. Many Mac users may already own BBEdit, but if you aren’t in that position, you should get TextWranger.
For Windows, I like Notepad++.
Both these editors allow you to have multiple tabbed windows open at once a number of helpful functions for dealing with code and for general editing. I’m not sure about Notepad++, but I know that TextWrangler has FTP built in.
I consider a good text editor an essential, even if you use a tool like Dreamweaver to do most of your work. I find, for the way I work, that I often open up pages in a text editor for various chores instead of using Dreamweaver – or in addition to using Dreamweaver.