http://www.htmlgoodies.com/ is a good site for learning HTML, it's got a lot of primers and tutorials, as well as a few advanced tricks for doing HTML.
Heres a little live-HTML renderer thing I had on my old blog, try this out as well.
http://htmledit.squarefree.com/
Just be careful, it renders right away, so if you put in an infinite loop, it might crash.