HTML editor

This is made by same people as BBEdit, but it's free:

http://www.barebones.com/products/textwrangler/

"TextWrangler is the “little brother” to BBEdit, our leading professional HTML and text editor for the Macintosh."

Or try gedit, it is free too and comes with loads of syntax highlighting including HTML:
http://projects.gnome.org/gedit/ (see osx d/l on the right hand side of the screen)

Or you can try PSPad (windows app) - wrapped as OS X app in my signature

I would recommend TextWrangler as essential for any Mac. It's an ideal text editor, and also allows easy editing of system files, handling the permissions and ownership issues.
It recognises a wide rang of scripting languages, colours syntax accordingly; it also uses regular expression searching and has extensive text manipulation tools.

RE: emacs...

Okay, I know I'm an antediluvian troglodyte, as my progeny always love to point out to me, but I'll add my two cents here and suggest "emacs" or its Aqua version "aquamacs" (emacs comes with Mac OS X and aquamacs is free).

Emacs is, in my humble opinion, the most powerful and flexible of all editors. You can do almost anything in emacs, not only writing and testing code in most any programming language natively, but also editing 10000 files automatically with a single line of emacs elisp code...

Okay, you may go ahead and make fun of me now ... I give you my permission.

Regards,
Switon

P.S. Barring emacs, then I agree TextWrangler is nice...