Google Docs

This can be a powerful tool when used correctly in the classroom.
Here are some ways you can you it:

• Real time editing
• Collaborating
• Buddy Edit
• Reader's Response
• Introducing spreadsheets
  

Here are excellent links :
http://sites.google.com/site/ctapvworkshops/Home/wikis/google-docs-in-the-classroom
http://edte.ch/blog/2009/10/21/introducing-google-docs-to-the-class/
http://googledocs.blogspot.com/