I have used wikis for several classes as a space for students to work on collaborative projects:

The British Literature Wiki

Summer Enrichment Program: Collaborative Research and Writing 2007

Summer Enrichment Program: Collaborative Research and Writing 2006

Teaching With Wikis: Lilly-East Conference

Here's an interview I gave on for a project on wikis in the classroom at the University of Delaware

Interview

Here's a link to the home page of that project:

Demystifying Wikis and Collaborative Writing