HTML information tends to come in two forms: language references and tutorials, and style guides.
The definitive HTML reference is the specification. Up to and including HTML version 2, these were handled by the Internet Engineering Task Force (IETF) under the Request for Comments (RFC) system. RFCs are available from several sites around the Web, but unfortunately there are over two thousand of them, on many different subjects. Dedicated RFC Search systems are useful for tracking down the one you need. A good place to start is RFC1866, which defines HTML 2.
From HTML version 3 onwards, this duty passed to the World-Wide Web Consortium (W3C). Versions 3.2 and 4 are currently available from the W3C; the HTML 4 recommendation is large enough to require compression in an archive! The latest specification is, however, explained with a great deal more care.
Away from the specifications, you may like to look at Web Review and Web Reference, two magazine-style sites that set out to serve Web Developers. Despite being obsessed with the latest excesses of Microsoft, Netscape, et al., they do cover the basic elements of HTML. Web Review has recently run a series of articles which focussed on a single element at a time, explaining all the possible variations and options.
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