I thought of some additional ideas. What do you think?

- Invitations

- A "materials needed" list for each class

- A public forum for general subject discussion

- A calendar

- Conferencing (with voice, video, images, chat)

- Buy books or supplies if needed

- For learning languages, there could be a service to chat with a fluent speaker

- To make tests, you can use something like Wufoo to make forms for tests

- Background theme for classes

- Progress charts

- Grade checker

- Mobile apps

- OpenID/other logins

- Citation helper

- Look up quotes and verses

- For whiteboard, maybe something with HTML5 canvas

- Group mailing list