If you've manage to hold out this long on Batman: Arkham Asylum, you've made a financially wise decision. PC gamers can get Rocksteady's fantastic Batman effort from Games For Windows On Demand for a pennies on the dollar.
Batman: Arkham Asylum is this week's On Demand deal, just $US12.49 USD or 75% off the original asking price, whatever sounds like a better deal to you. Considering the accolades Rocksteady received for their surprise hit, including a buy out from Warner Bros., that's a pretty good deal on a not too old game. Of course, you'll need to do the GFW Live Gamertag and client download thing, which could alter your opinion of the sale.
Better buy it now if you have any intentions of playing the sequel, which certainly could come to the PC as well.
Get Batman: Arkham Asylum at 75% Off! [Games For Windows - thanks, Jambes!]