Below I have listed a number of resources that I have found particularly useful in my own ongoing exploration of HTML as well as for my students' reference. Since all these are external sites, I can not guarantee that a site will continue to be available, nor the accuracy of the information contained therein.
Jakob Nielsen's The Alertbox: Current Issues in Web Usability
(of which, I highly recommend reading: Top Ten Mistakes in Web Design)
The following are URLs of ftp sites where commercial, shareware and freeware HTML editors can be downloaded directly from the Web.
W3C Tools for WWW Providers (including HTML editors, filters, and converters)