You can donate your idle pc's computational powers for various scientific enterprises. 420chan has a nice faq/overview of this here (http://taimapedia.org/index.php?title=420chan_BOINC_team)
I have created a FFhacktics team for the World Community Grid. (http://www.worldcommunitygrid.org) This one specializes in medical and humanitarian projects. Download, make an account, and then join the team. The Team can be found here (http://www.worldcommunitygrid.org/team/viewTeamInfo.do?teamId=DRVJ8M31Z1).
I can make more teams for the various other projects if you guys wish to. You can find a giant list of such projects here (http://en.wikipedia.org/wiki/List_of_distributed_computing_projects):