Excerpt from Peter Flynn's book, The World Wide Web Handbook . Ins and outs of HTML specifications, DTDs, etc., as well as an introduction to HTML markup. Introduction to HTML by Eric A. Meyer and Case Western Reserve University. The most novel aspect of this site is the interactive quizzes which follow after each chapter. Intermediate HTML by Eric A. Meyer and Case Western Reserve University.
Primary focus is on creating forms.
HTML Reference Manual by Sandia National Laboratories. A Guide to HTML Commands by Richard Rutter. Fairly complete A to Z reference. Introduction to HTML by Ian Graham. Excellent A to Z reference.