I am not sure if this is what you are looking for...
Like Jeremy, I thought of Yudu which I have found very easy to use.
I used it to give examples of our use of a Wiki in Maths.
Grace I hope it's useful.
My main blog has lots of maths links, do your math teachers use WolframAlpha at all?
That is one amazing resource! There is a link here to resources younger students can try.