PBwiki is a really great free, hosted wiki service for people who want to quickly create wikis that are easy to configure and maintain. Wikis are really starting to come of age lately (just look at the popularity of Wikipedia), but many people either do not have server space to host a wiki or the time, resources or experience to properly install and configure a wiki, so PBwiki is a really great way to get started creating wikis. As they say on their website, you can make a wiki as easily as a peanut butter sandwich.
PBwiki was started by my friend David Weekly as a project he created at the very first SuperHappyDevHouse in May 2005 and now David and the PBwiki team are hosting over 100,000 wikis. The BarCamp website was one of the first places I came across PBwiki and now I’m seeing them all over the place. Rock on PBwiki!
UPDATE: David Weekly has just informed me that The Un-Official __Snakes on a Plane__ Audience Participation Wiki is hosted on PBwiki.