I was recently shown a link to RationalWiki - a pro-science and anti-pseudoscience wiki, which also covers a host of other topics, such as politics and debate. RationalWiki serves as a counter to wikis that post extremist and/or fringe nonsense. One excellent article I came across on the site was about the conspiracy theory that the Moon landings are a hoax:
I think the article provides an accurate account of the origins of the conspiracy theory as well as gives good counter-arguments against it. My favorite would have to be the part about the US "propping up" the Soviet Union was simultaneously wanting to "humiliate" it - that alone shows the absurdity of how the hoax advocates sound. That, and it's ridiculous to think the US bribed every single country to keep quiet. The obvious explanation is: The Moon landings were real.
(Note that RationalWiki is not connected to Wikipedia. Both sites are wikis, however; see Wikipedia's definition of a wiki for more information.)