The bundle is made up of five pretty rad indie games: Braid, Cortex Command, Osmos, Machinarium, and Revenge of the Titans. Sold separately, you're looking at $85 worth of stuff here. With the Humble Indie Bundle, you get to name your price for the whole shebang. Yup, you can be a disgusting cheap skate and get all 5 games for just a penny if you really wanted to and could live with yourself afterward. Extra cool points for the fact that you can split up your payment so that it ends up in the hands of up to 4 different entities: the developers of the games themselves, the Humble Bundle folks, the excellent digital rights group EFF, or my personal favorite, Child's Play.
If that's too philanthropic for you, then just get the Bundle on the cheap because the games are good, you bastard.