Free HTML editors are often considered the best kind. They offer flexibility and power without an outlay of cash. But beware, if you're looking for more features and flexibility, there are many reasonably priced HTML editors available. Find the best HTML editor for you.
Aptana IDE is an interesting take on Web page development. Instead of focusing on the HTML, Aptana focuses on the JavaScript and other elements that allow you to create Rich Internet Applications. One of the things I really like is the outline view that makes it really easy to visualize the DOM. This makes for easier CSS and JavaScript development.

KompoZerKompoZer is a great WYSIWYG editor. It is based on the popular Nvu editor - only it is called the "unofficial bug-fix release." KompoZer was conceived by some people who really liked Nvu, but were fed up with the slow release schedules and poor support. So they took it over and released a less buggy version of the software.

NvunVu is a great WYSIWYG editor. I prefer text editors to WYSIWYG editors, but if you don't, then nVu is a great choice, especially considering that it's free. I love that it has a site manager to allow you to review the sites that you're building. It's surprising that this software is free. Feature highlights: XML support, advanced CSS support, full site management, built-in validator, and international support as well as WYSIWYG and color coded XHTML editing.
Amaya is a bit hard to use, but it's endorsed by the W3C, so you know that pages you build in it will be standards-based. It offers features like CSS editing and will edit XML really well. Feature highlights: XML support, scripting support, advanced CSS support, built-in validator, and international support as well as WYSIWYG and color coded XHTML editing.
SeaMonkey is the Mozilla project all-in-one Internet application suite. It includes a Web browser, email and newsgroup client, IRC chat client, and composer - the Web page editor. One of the nice things about using SeaMonkey is that you have the browser built-in already so testing is a breeze. Plus it's a free WYSIWYG editor with an embedded FTP to publish your Web pages.
Arachnophilia is not free - it's "careware", but just because you don't have to pay cash for it doesn't mean it's not a good product. In fact, it's a great text HTML editor with a lot of functionality. The color coding makes it easy to use. It may or may not work on Mac and Unix. Feature highlights: Color coded XHTML editing.
NetBeans IDE is a Java IDE that can help you build robust Web applications. Like most IDEs it has a steep learning curve because they don't often work in the same way that Web editors do. But once you get used to it you'll be hooked.
Smultron is a very simple HTML editor for the Mac. It offers text editing and HTML validation as well as extended search and replace across multiple files.
Taco was recommended to me by some readers, and when I checked it out it does seem to be a full-featured text editor for Macintosh.
TextWrangler is from the same company that makes BBEdit. If you can't afford BBEdit, you might want to look into Text Wrangler. It's a text editor, but it does work well for Web page editing. Feature highlights: color coded XHTML editing.
Would you buy one if you could afford it?