Reddit runs the largest Secret Santa in the world.
The concept is simple. You sign up, fill in a simple form, state what you like/dislike, and receive someone else's information when it's live.
Over 58,000 people have registered so far this year.
What would it take to have a secret santa for your community? How much fun/activity would it generate? Probably quite a lot.
It's simple to execute (talk to your tech person) and great for a community bonding experience. You might not get 58k, but you should still get a dedicated core group of members.