What is a wiki? Check out this video.

Tools to Create Wikis

Wikispaces Ad-free wikis for education.
Wet Paint Wikis also provides ad-free wikis for educational purposes.

Examples of Classroom Wikis

Math 8 Geometry
Grade5/6 and Grade 2cooperated to make this alphbet wiki of their hometown.
Grade 7 and 8 The greatest rock stars of all time.
Grade 6 Study Skills
Grade 3 Choose your own adventure story
Mrs. L's Collaborative Learning This links to an adaptations page--others are on the left hand side.
Grade 7 and 8 Studying Societies wiki