I recently set up a wiki for my students through http://pbwiki.com. I planned on introducing it after I worked out the kinks and became more familar with it. However, I may not use it after reading about Wetpaint Wiki (www.wetpaint.com/education) on Hey Jude’s blog. Check it out! 
How can wikis be used in the classroom?
Group projects: Students work together in one place to research, outline, draft, and edit projects within the wiki
Assignments: Post homework, course materials, study guides, and more.
Resource Collections: Organize articles, websites, videos, and other resources for students
Peer Review: Post questions for student brainstorming, or have students post papers for peer feedback
Group FAQ: Students and/or teachers post and respond to questions on a given topic
Parent Involvement: Give parents a chance to be a part of the classroom and stay up to date on classroom news and events
Online Newspaper: Create a student-published online newspaper
Wetpaint Wiki in Plain English
I think I just figured out what my next Gilmore night lesson needs to be on.