Not entirely easy going, but very interesting for the insatiably curious. A guide to writing good HTML documents. Contains pointers to other information about good style. A bit pedantic, they advocate a style which seems to me to be excessively fussy. However, there are many good ideas and this is well worth reading.
Every recommendation is backed up with references to the research literature.
A commercial newsletter service devoted to the use of the Web in K12 education. Covers distance learning as well as classroom instruction. The newsgroups are regular netnews groups, but you get a managed and filtered gateway. Unlike the more common HTML offerings on the Web, this is a tutorial rather than a reference. It is a subset of what is offered here, but it is quick, short and it is free.