A long time ago, I made a little web app that allowed you to submit Latex code to a server, the server would run pdflatex and then send back the pdf to be rendered on the page.
Nowadays MathJax can render LaTeX equations in the browser. I found http://www.texrendr.com that let's you interactively write formulae, but it's restricted to a single equation. There's also the LaTeXit standalone app, but you have to keep hitting "typeset". This isn't so useful if you're trying to quickly type math during a Skype call.
So I wrote a little program to run in the browser:
http://www.cs.toronto.edu/~jacobson/latex.html
You can also fork the git gist