It's free and easy to contribute either a small correction or whole pages. You just need to be able to cite references. If you can add a resource to the page, you can even link directly to good skeptical websites for people. You don't need permission, and with simple edits, you don't need any coding skills.
Best of all, it’s rewarding and fun to use your skeptical knowledge to enhance an essential public resource. Furthermore, we know from our internal traffic statistics that people really do follow up on the skeptical resources cited in Wikipedia articles.
Tim Farley gives an in-depth primer on Why Skeptics Should Pay Close Attention to Wikipedia.
You can read a rundown of some basics and rules, as well as get a bunch of useful links on how to get started here.
The Wikiproject Rational Skepticism is an association of skeptical Wikipedia editors. They vigilantly keep track of articles to make sure vandalism doesn't happen. When it does, they make sure someone can go in and fix the problems quickly to get the right information back up on the site.
Another project is the Skepticwiki, which is a standalone site devoted exclusively to skepticism. It shares the wiki encyclopedia format.
Many skeptical topics are well covered on Wikipedia. But where a skeptical eye is really needed is in paranormal topics.
When people turn to Wikipedia for information on iridology or “reptoids” or chiropractic, that article may often be the only source they consult. Or, if they do consult further sources, these may often be the sources cited in the Wikipedia article. Either way, paranormal proponents have been quick to load Wikipedia with content and citations that are friendly to their own claims. Sometimes, these articles are virtual commercials for paranormal industries. In those cases, skeptics can perform a valuable public service by bringing paranormal articles up to the NPoV standard with descriptions of skeptical criticism and references to relevant skeptical sources.
On lesser-known subjects, paranormal proponents have the freedom to make sweeping, biased, and wildly unsupported claims. These low-quality articles stand unchallenged until a skeptic eventually happens to review them. Finding and fixing these is fun and satisfying for skeptical editors. Because those articles are so bad, they are easy to improve — and edits will tend to stand for a longer time.
If you have suggestions for topics to edit, or if you have edited articles, let us know!