A challenge recently posted on Innocentive seemed to me like something that may interest many LWers: "Models Motivating and Supporting Altruism Within Communities", with a grand prize of $8000. To quote from the challenge:
We are interested in looking at novel concepts from nature, business, or other areas that may elucidate the dynamics that help promote and maintain altruistic behaviors.
Further details are available on innocentive.com. I think that it would be a nice opportunity for our LW decision theory experts.
[For anybody who decides to participate: the links I provided contain a referral string so that, in case you win a prize, I can match your donation to the SIAI with the same fraction of my referral award ;) Please use them to register.]