We are using wikis to collaborate with another school in our district around the topic of animal adaptation. We participate in the Voices of the World Project and the Winter Wonderland project. We will be collaborating using Google sites on an Alien exchange project with a school outside our district. We are a K-5 school and are open to finding more schools to collaborate with on curriculum related objectives.
I can't show you an example because my wiki is closed, but using Wikis is a great way to stimulate collaboration. I use wetpaint and set them up as private so only users I invite can access. Then students can collaboratively create documents, brainstorm ideas, etc . . . If anyone uses it inappropriately, I simply ban them and they no longer can access it.
I teach maths and science (Year 7 and 9) at a small rural school in Victoria, Australia. We are using a wiki at "On Line Science Fair" to share our student science projects. We are also involved with a Maths Connections wiki (for all ages) sharing data and graphs on Voicethread. You will need to join both sites if you are interested in having a look.
What subjects and age students are thinking of?