This is not strictly programming related, so I apologize. But I think this fits within the scope of this site.
We have a community site (part forum, part wiki, part knowledge base) where our users can participate in discussions, Q&As, etc. One of the things I would like to do is have some type of reward system where users feel like they are gaining something by participating. And something that gives them the incentive to come back.
Stack Overflow has reputation and badges. Digg, Propeller and Reddit have their own systems whether that be points, karma or whatever. I am thinking something that has some RPG style elements but I can't think of any good examples.
Does SO have any ideas that could be useful in this scenario?