Texify - Online LaTeX equation writer

Nice. I love URL interfaces (phras.in is another good one). Definitely useful for tutoring over IM.

Font looks a bit cartoonish though...

http://texify.com/?$\int_a^b\left(\frac{\partial%20L}{\parti...

Or http://www.codecogs.com/latex/eqneditor.php

There is also http://mathbin.net/

check out http://www.pastemath.com that has been around for 5 years now.