Some of the examples below were found through exploring the web, some were found in Will Richardson's book (see Books (including e-books))
A collaboration of sites and sounds: using wikis to catalog protest songs - This is a very clear example of how a wiki can be used for learning and assessment. It includes a full lesson plan.
The Blended Learning Unit at the UK's University of Hertfordshire has produced a series of Business School case studies of Wiki use
The following video is a 55 minute lecture, in which Richard Buckland describes how he incorporates wikis into his own teaching. I found this to be both highly informative and inspirational.