Wikis are a very powerful and interesting web development for the collaborative collection and sharing of information. The 900 pound gorilla of wikis (1,534,606 articles in English today!) has to be Wikipedia, which never ceases to amaze me. Case in point: the detailed and illustrated article on STS-116, the still ongoing space shuttle mission! There are even notes on day 5 of Discovery's mission (today). While there is no shortage of web sites with information on NASA missions (including NASA's own), the point is that you can find almost anything in Wikipedia, in a standardized format, usually with many links and references.
Of course Wikipedia isn't the only wiki - there are many of them, including a wiki devoted to the Orbiter space flight simulator, orbiterwiki.org. I've heard about this wiki for some time but visited it for the first time today (linked from the Wikipedia article on Orbiter, which I was editing), and it has a lot of interesting, useful, and easily accessible content.