elearnspace links to Barbara Gross Davis's Tools for Teaching: Collaborative Learning: Group Work and Study Teams. Could be a good resource for getting teachers thinking about collaborative learning.

Side note: One of the things I looked for in the bibliography was Kenneth Bruffee. I haven't researched that much on collaborative learning outside of Rhet/Comp, but in what I have seen, I never see any of his work mentioned. "Collaborative Learning and the 'Conversation of Mankind'" was a pivotal work for me (and our field).