I'm not sure if this is exactly in the frame of your question, but Mathematica could be useful.
You could edit the notes in a Mathematica notebook (a very easy task), and then save them to HTML. By default the mathematics are saved as .gif images, but it does have the option to export to X/HTML+MathML. I think gifs are fine, though.
Here's a screen shot I took. On the left is a Mathematica notebook that I just wrote up. On the right is the output HTML version in a web browser.
As you can see, the reproduction is very faithful.
Here's a picture of Mathematica's "writing assistant" to give you an idea of the sorts of formatting you can do:
And of course, you can always just highlight a piece of a Mathematica notebook, right click, and Copy As LaTeX. Example using the Ramanujan identity:
$\int _0^{\infty }\frac{1+x^2/(b+1)^2}{1+x^2/(a)^2}\times \frac{1+x^2/(b+2)^2}{1+x^2/(a+1)^2}\times \cdots dx=\frac{\sqrt{\pi }}{2}\times \frac{\Gamma \left(a+\frac{1}{2}\right)\Gamma (b+1)\Gamma \left(b-a+\frac{1}{2}\right)}{\Gamma (a)\Gamma \left(b+\frac{1}{2}\right)\Gamma (b-a+1)}$