One of the cool tools that I like to use is Nvu, an HTML editor and web site management tool based on the Mozilla code. Daniel Glazman is the inspiration and wizard behind Nvu.
Nvu is very easy-to-use. It provides multiple editing modes (WYSIWYG, tags, source, preview). I rarely need to use anything other than the WYSIWYG (Normal) mode but it is easy to switch to source mode when I need to tweak something. Nvu also supports advanced features such as CSS, JavaScript and configurable toolbars. I find it particularly good at dealing with tables (e.g., one-click to delete a row or column).
Unlike Mozilla Composer, which Daniel and I worked on together, Nvu goes beyond basic page editing and includes a site manager sidebar to help you manage an entire web site. Like Mozilla Firefox, Nvu supports extensions such as Launchy.
Developed by Disruptive Innovations, Nvu is an open source project sponsored by Linspire. It works on all major platforms (Mac OS X, Windows and Linux) and it is free. You can download it from here.
Tabbed editing is also a cool feature of Nvu, although I have to admit I am more likely to use a text editor like vim to edit HTML or CSS code.
I have been using NVU for about 6 months, and although it has a few bugs, I have found it to be a great introductory tool to web design. I only started builind web pages in June this year, and a friend recommended NVU. It is far better than any other free or trail HTML editor that I have come across. Shame some bugs means I have to close and reopen it sometimes, but apart from that it is perfect for my needs.