There are literally hundreds of wikis to choose from. Here is a breakdown to help you choose:
(Please note this page is under construction!)

Name of Wiki	URL	Pros	Cons	Recommendations
Wetpaint	www.wetpaint.com more info here	Nice layout Easy to use Ad-free for educators	User IDs require email address Users must be at least 13 years old	NEVER use student last names High School only get parent permission for wiki use and an email account usage set wiki to private
Wikispaces	www.wikispaces.com	Ad-free No email address required for students IDs Designed with educators in mind	Layout not as nice as others Setup could take longer Not as many bells & whistles	NEVER use student last names get parent permission for wiki use set wiki to private
PB Wiki	www.pbwiki.com more info here	Ad-free one password for entire site no email address required for students still able to track users contributions	advanced controls are only availabe with premium subscription ($9.95/month)	NEVER use student last names get parent permission for wiki use set wiki to private

• Writing Wiki is a free online writing spaces for college students or others who love writing. Because it's a fairly new site, Writing Wiki does not attract significant numbers of readers. Writing Wiki sponsors student writing and original research.
• Wikipedia
• Wikibooks
• Teaching Wiki is a free space for teachers to brainstorm about pedagogy, research, and theory.
• Wetpaint: www.wetpaint.com
• PB Wiki: www.pbwiki.com
• Wikispaces: www.wikispaces.com (ad free for educators)
• Zoho Wiki: www.wiki.zoho.com
• Media Wiki (software): MediaWiki is a free software wiki package originally written for Wikipedia.

• Dokuwiki (software)