Wikis
Instructors may set up a wiki at Wikispaces (www.wikispaces.com) or Google Docs. A lot of wiki hosts have commercial advertisements and pop-ups that are distracting. An alternative site that is geared towards academic wikis is www.wikieducator.org/Main_Page.
A great easy-to-use wiki is Google Sites at http://www.google.com/sites/help/intl/en/overview.html