Library Instruction Wiki (Mediawiki)
Library Success: A Best Practices Wiki - "one-stop-shop for great ideas and information for all types of librarians" (Mediawiki)
LIS Wiki - library and information science encyclopedia (Mediawiki)
Digiwik: The Digitization Wiki - repository of digitization information for use by individuals, museums, libraries, researchers, and any other entities with digitization needs (Mediawiki)
LibLand - "This wiki gives new librarians and library school students a place to find information and a place to add information about libraries, library school, the American Library Association (ALA) and what it's like to be a new librarian."

Other wikis of interest

Librarians blogging about wikis

Using wikis for collaborative company research - Library Voice (6/8/2006)
More Mediawiki Mayhem - Library Web Chic (6/5/2006)
Adding a WYSIWYG editor to Mediawiki (part II) - Library Web Chic (5/25/2006)
Wikis in the University Library - by Michael Stephens on ALA TechSource (5/22/2006); interview with Chad Boeninger, Reference & Instruction Librarian at Ohio University
Moving Mediawiki to a production server - Library Web Chic (5/17/2006)
Extending Mediawiki - Library Web Chic (5/8/2006)
Installing a WYSIWYG editor in MediaWiki - Library Web Chic (5/1/2006)
Wikiperiments - Library Web Chic (4/20/2006)
Wikis for the rest of us - from Digital Reference (2/3/2006)
Wiki Woes - from The Industrial Librarian (1/25/2006)
SJCPL's Subject Guide Wiki - from dave's blog (12/8/2005)
Wikis as handouts - from Digital Reference (11/13/2005)
Our reference wiki and online tutorials - from Digital Reference (10/28/2005)
PBWiki - from See Also (10/13/2005)
Where I've been lately - from Digital Reference (9/30/2005)

List of wiki software - from Wikipedia
Wiki Engines - from WikiWikiWeb
Top Ten Wiki Engines - from WikiWikiWeb
Wiki Engine Popularity - from WikiWikiWeb, wiki engines ranked by number of Google search results
Wiki Choicetree - from WikiWikiWeb, wiki engines sorted by features

WikiMatrix - interactive comparison chart (you choose the software to compare)
Comparison of wiki software - from Wikipedia
Comparing Wikis - from WikkiTikkiTavi
Challborn, C. & Reimann, T. (2005, July). Wiki products: A comparison. International Review of Research in Open and Distance Learning, 6(2).

WikiMatrix - in addition to an interactive wiki software comparison chart, this site also features a discussion forum about wikis
RecentChanges.Info - "all things .wiki" blog
wikiSquared - blog
WikiLand
International Symposium on Wikis
HTML::WikiConverter - convert HTML to wiki markup
Wikis - Virtual Reference Special Interest Group (related blog post)