This is a great beginning tutorial which covers all the basics in HTML including tags, text structure, lists, anchors, and images. It also includes an HTML lab to test out your own markup.
W3School's HTML Tutorial
A very thorough guide. Read the explanation for tables and try
the interactive examples.
HTML Teaching Tool
A comprehensive HTML guide from Webmonkey. Each page includes a
description of the web element, examples, and a practice session for you
to enter your own code.
Webmonkey’s HTML Cheatsheet
Print this reference sheet for your notebook. It has every HTML tag
you will need to know.
W3C QA Recommended list of DTDs
Copy and paste your DOCTYPE declaration from this page into your
HTML document above the html tag.
Markup Validation Service
This is the W3C Markup Validation Service, a free service that
checks Web documents in formats like HTML and XHTML for conformance
to W3C Recommendations and other standards.
W3C: The global structure of an HTML document
This is an extremely thorough explanation from the
World Wide Web Consortium of the structural elements of an HTML
document and their corresponding tags. This includes every single
tag available in HTML 4.0.