Free Technology 4 Teachers. This is a nice site to use for creating a wiki that can be collaborated on w/ others. A pad can be set to public or private and has a variety of nice features such as: color scheme (to see who wrote what), creating links, task lists, and the ability for everyone to be emailed when changes are made (ie, Wikipedia).
I recommend checking out Hackpad by clicking here!!
For my top 10 sites for creating a wiki click here.