Like Google Docs, try this:

I have become quite a fan of Google Docs, how wonderful is it to have a place were you can write down your ideas on some project and then share it with other who can add their own contributions. I have found it to be a valuable tool in group projects, because it is hard to always be able to get together, so Google Docs provides the environment to come together with all our ideas in one place. No need to worry about lost emails anymore, it is all right there. 

However, there is an other online collaboration tool that I really like to use: Prezi.com. It is actually advertised as a presentation tool, sort of like PowerPoint but not really. However, it has the wonderful ability of allowing multiple contributors on the same presentation. This tool can be easily incorporated into the classroom environment. Students are always asked to do presentations for classes, so why not have them try out something different from PowerPoint. They can put all their ideas down on the Prezi canvas, and then decide what ones they want to present. Again, no need to attach PowerPoints to emails and worry about formatting issues between computers. It's fabulous!