or perhaps we could gamify THIS forum.....
You can use this mechanics - XP, levels, achivements, statuses, power, leaderboards.
Select what you want users to do (create topics, answer, etc), set points for this actions. If player earn some quantity of points he gets level up, or even became moderator.
Have you read the book "Gamification by design" ? There are example how to gamify forum.
Also stackoverflow is good example.