I am working through the past exam papers available for my course. I am then making them available for collaboration using Google Docs.
However, for maths heavy material, the Google Docs equation editor sucks. In fact the MathJaX support on Mathematics here on Stack Exchange is much better.
I am looking for an on-line editor for equation heavy documents that supports collaboration and sharing, and supports LaTeX.
Notes: I am currently reviewing the solutions suggested here; http://en.wikibooks.org/wiki/LaTeX/Collaborative_Writing_of_LaTeX_Documents
Google Docs is actually quite good. If they just supported a keyboard short-cut for inserting an equation, and had some sensible text in equation selection behaviour.
latexlab.org, but it's not a WYSIWYG editor; just an online IDE for LaTeX really (unless I missed something).
zoho documents is another service I might look at.