I agree that it is very beneficial to understand HTML, and it is quite easy to learn.
However, if you're looking for a tool to help you design a site, Dreamweaver is very good. I have especially found its template feature useful. It enables you to create a large site based on a template, and when changes are made to that template, they are made to all pages based on that template. This can save alot of time in editing work. Of course, these sorts of things could be done using Server Side Includes or PHP or something, but for starters, the template feature is powerful.
Homesite is also a very useful text editor, and as it was mentioned earlier, comes bundled with the PC version of Dreamweaver.