GoogleDocs is one of the tools I like to use in my online classes. Students know the name (i.e., Google), the interface is easy for them to intuit, they can share documents via simple URLs, and it’s integrated with the Google Apps for Education.
Today, the Google Docs blog announced an improvement to the collaboration feature, so it’s easier to create groups. Previously, you had to manually add email addresses each time you wanted to share a document; now you can simplify the process by using the contact manager to create groups.