I\'m not asking about converting a LaTeX document to html.
What I\'d like to be able to do is have some way to use LaTeX math commands in an html document, and have
Historically, rendering the LaTeX and extracting an image has been your best bet for cross-platform, cross-browser math stuff. More and more, MathML is becoming a reasonable alternative. Here's an online converter that will emit MathML from Tex markup, which you can then embed in your webpage. I know Gecko-based browsers like Firefox and Camino play nice with MathML, as does Opera. IE doesn't work out of the box, but there are plugins available (like this one).
Texvc is a great find! The vanilla HTML output should work well if you're mostly interested in superscripts/subscripts/italics/common symbols, but for more complex things, be aware that the most popular math-oriented sites out there (e.g. Wolfram) generate images, so there may be only so much you can do if you're interested in cross-browser compatibility :-(