I just joined Giving What We Can, which means I've pledged to give at least 10% of my income to the most effective charities helping people in developing countries from now until I retire. While this was already something I was doing and planning to do, it's nice to have signed my name to it.

(I would have joined back in 2011 but back then I was doing the risk-neutral stock options thing and didn't qualify.)

Update 2014-08-25: on July 11th 2014, I raised my pledge to 30%.