I was using the built in equation editor used by Pearson's "MyLab and Mastering" physics course, and I really like how it's both interactive and uses Latex syntax to insert equation elements. Screenshots are shown below:
look what happens when I complete the "\sqrt"
The Latex syntax works for greek letters, superscript, etc., and makes it easy to add equation elements without having to click through a dropdown list (though it still provides one for convenience). The interactive editor view is easier to understand than pure Latex, removes the hassle of trying to match all those brackets when writing Latex, and also makes it easier to edit equations afterwards. For example:
I can hit backspace once to delete the whole thing! Compare that to the Latex equivalent
which takes 44 backspaces :O
Anyways, I guess the question is, is there an online equivalent? This is by far the fastest equation editor I've used, but the only thing this editor lacks is Latex export, which renders it useless for anything besides submitting answers to my physics homework :(