MathJax, the new cool for mathematical display on the web
MathJax allows writing equations directly in LaTeX or in MathML and renders them either in MathML in browser that supports it or with more common elements of HTML and CSS.
It is used notably by the CERN, several sites of StackExchange, and friends. It's also supported by the AMS and the IEEE.
What's more this is somehow the successor of jsMath that I was using for my little experiment in literate programming. And since Sphinx now has a plugin for it, I've just updated my literate musing pages (refreshing the theme at the same time to a get a lighter and hopefully more readable display).