Some of you will have heard about SETI@Home, which uses your computer's spare CPU cycles to help search for extra-terrestrial intelligence, but fewer are aware that the same technology is being applied to help find cures for Alzheimer's, Mad Cow (BSE), CJD, ALS, Huntington's, Parkinson's disease, and many Cancers and cancer-related syndromes.
It's easy to do, and won't cost you anything, except maybe a few cents' worth of electricity. Just go to Folding@home (folding.stanford.edu) and download and install the software.