The Ignite! wikis site has general information on wikis as well as good examples of wikis that are used in the classroom (from BPS and elsewhere).
http://ignite.wikis.birmingham.k12.mi.us/wikis

Here's a list of all the classroom wikis across the district:
http://www.wikis.birmingham.k12.mi.us/

This site has some ideas about how to start incorporating wikis into your instruction.
http://www.teachersfirst.com/content/wiki/