Wikis that you should check out...

1. Wikipedia was the first major wiki and still one of the most browsed.
2. Conservapedia was produced by Andy Schafly, believing that Wikipedia was "full of liberal bias." It does provide a good amount of alternative views, I'll give them that.
3. Encyclopedia Dramatica is the main wiki for most of the "chan" boards. The best place to go for info on online memes. (Warning: Not safe for work or school! Deleting your cache and browsing history after viewing is highly advised.)
4. Wikia is basically a hosting-service for wikis covering entire topics.
5. Wikileaks allows you to view (and submit!) sensitive information. They even supply methods of viewing the site and submitting content securely.