I heard about the world community grid in New Scientist and have now downloaded it. It's one of those programs like SETI@home that uses the spare processing time on your computer and those of thousands of other home users to do research and data processing that would otherwise require a bank of supercomputers. The twist on this one is it chooses what projects to work on specifically for their potential benefit to humanity - medically, socially and environmentally.
Seems like a nice little way to contribute to the common good at no cost to oneself. Edit: Just for fun, you can also join a team and you get scored together on how much processing your team has done. So I've joined the Livejournal bloggers team.