Share 'Wonderfully Educational Wikis'

I am working my way through the web looking for examples of wikis to share with participants in my workshop and online session. If you have seen a good example of a class wiki, student wiki, teacher wiki or school wiki.....or even one that does things just that little bit differently.....I'd love to hear about it. Drop me a line or 2 here and add a link to your examples. Thanks, Deb