As far as altruistic gaming marathons go, we can't think of any quite as ambitious as this: Speed Demos Archive
, a group of gamers who've trained their thumbs and minds into razor-sharp, game-beating machines, are currently attempting to beat 100 games in four days. If you feel like rewarding the group for their tenacity, you can make a donation, all of the proceeds from which go directly to the Prevent Cancer Foundation. Lucky givers might even receive a special prize relating to whatever game the group is currently plowing through.
It's still pretty early on in the proceedings -- early enough that their sanity hasn't yet been utterly decimated. Check out the Speed Demos Archive's official site
to watch them devour some great games, or check out the marathon's official page
for a speed run schedule.