Wikis traditionally reward contributors with prestige, or often just warmth and fuzz (as it is hard to see WHO is the main contributor and thus gain prestige).
The BitCoin (open source digital cash alternative) Wiki has created a reward system. Short version: they’ve created a “game” whereby you earn points by your contributions to the wiki. Periodically they take money donated to the Wiki and disperse it to the contributors proportional to their relative score in the “game.” Interesting idea!
Full details at: Bitcoin:Contributors award – Bitcoin.