If you haven't checked it out yet, check out MSDN Library's Wiki! It is the full MSDN Library, but allows the community to add comments to the end of each article.
Some may argue it's not a "true wiki" in that you can not edit the original article or create new articles, but I think this is a good adoption of the community involvement in a standardized library.
David Kean Rocks!
I'd like to specifically point out that I just found out that David M. Kean, an SDET on my team, is the #1 top contributor! He has almost 450 posts, about twice as many as 2nd place and almost 4x as many as 3rd place.
David was (and still is) big in the FxCop community before he was snatched about a year ago by the FxCop team and now works in my product unit, Team Dev (we make Visual Studio Team Edition for Software Developers). He has a strong passion for the community and now runs our VSTS chats. Thanks for your continued impact in the online dev community David!