For those of you who are thinking about buying Batman Arkham Asylum but were holding out may want to read this article over at Joystiq. It would seem that the game is on sale through the Games for Windows' Games on Demand for only $12.49!
That is dirt cheap and well worth the price in my mind. The only sticking point is the GWL Games on Demand service, I have not used it so I have no idea how it works compared to Impulse or Steam. Batman is one of the few GWL enabled games so it's a bonus if you are into achievements.