A free system to create social media in the classroom – available to download – that includes “integrated forum, blog, comment, wiki, chat, social bookmarking, RSS, microblogging, widgets , and video commenting are the first set of tools. … curricular material: syllabi, lesson plans, resource repositories, screencasts and videos.” It’s based on Drupal, which I find difficult to use (setup and customisation expecially) from a techincal point of view, but most of this is done for you here. [link]
Moodle is also well worth a look if you’re into this kind of thing. I’ve been digging in a lot lately.
It has an insane variety of plug-ins for its modular model and a massive, active community behind it.