The way I have used a Wiki was already posted as Idea #58. I currently have students find online resources which complement the materials in the class. this material can then be used by future classes to help their projects. It really worked well in a animation class where students were able to use found models in their animations. The students created a very intensive wiki showing locations, and reviews of different model libraries online.
The Idea that I thought of was to have a glossary that is made up by students. It could have some key terms listed, and students would fill in definitions, they could also add additional terms and their meaings. This Wiki could continue to grow with each set of students, or could be reset so each set of students could start over.