HTML, or Hypertext Markup Langauge, is the primary language of the web. WYSIWYG editors like FrontPage, Dreamweaver and GoLive are pretty interfaces that keep you from looking at the code itself, but the more you understand it, the greater control you'll have over your web pages.
I do use WYSIWYG editors (Dreamweaver Ultradev 4, currently) for content management, but not for the original page design. When I'm creating or redesigning a web page, I very much prefer to see the code directly. I'm lucky to have Visual SlickEdit as a text editor, but I'm happy to use plain old Notepad too.
If you've never stared code in the face before, you can right-click (on a Mac, control-click) on any part of a web page that isn't an image or multimedia component, and you'll see an option to "View Source" or "View Page Source". Do it on this page, and you'll see the code that makes the page work. It's the best way to find out how somebody did something on a web page.
Here you will find resources to learn about HTML, some particularly useful HTML tools for web design, and a place to check your web pages to see if they meet HTML standards.
HTML 4.01 SpecificationThe current HTML specification is version 4.01 (no relation to the browser versions). Though it takes some time before you start to find your way around, this is the reference to consult when you want to know what HTML can do.
Useful HTML TricksThe first three topics are about controlling the layout of your web site. The last is an easy trick for a splash page that can set a tone for a web site before taking the visitor to the main page of the site.
HTML ValidatorCurious to see if your HTML coding is up to speed? Visit the HTML Validator, sponsored by W3C. At this site you can enter the URL of a web page and it will tell you if you are using HTML correctly. A great learning tool for the obsessed.
XML 1.0 SpecificationXML, Extensible Markup Language, is one of the next big things in web technology. XML provides the means for authors to describe the quality of content. As the web becomes more dynamic, the ability to qualify data will be essential. W3C released the XML 1.0 Specification in February 1998, and you can find articles through many of the developer resource sites including an XML FAQ from Peter Flynn and "XML Does it Your Way", an introduction from webreference.com.
I'll be adding an XML section to this site shortly, to cover this major jump in web technology.
For HTML 4.0: