There's a young movement that combines the idea of a duty to help others with the idea that you should maximize the impact of your actions. It has been given many names, including

I want to be able to say things like the "X movement" or "I'm organizing an X discussion", but I'm not sure what name to use. Suggestions? I'm currently leaning towards "Smart Giving" or "Effective Giving".

Update 2013-02-28: The community seems to have standardized on "Effective Altruism".

Update 2014-03-11: Will MacAskill wrote up a history of how the Center for Effective Altruism got its name, which is probably much of how the term "effective altruism" came into use.

Update 2014-07-26: I found a use of "effective altruist" on one of Eliezer Yudkowsky's 2007 Overcoming Bias posts (now redirects to lesswrong): "If you want to be an effective altruist, you have to think it through with the part of your brain that processes those unexciting inky zeroes on paper, not just the part that gets real worked up about that poor struggling oil-soaked bird."