[Update] Remedy has revealed to Joystiq that Alan Wake's American Nightmare will be released on both Steam and Good Old Games on May 22. Both Steam and GOG.com, which just added Alan Wake to its DRM-free library, are holding sales for the original title.
American Nightmare is available for 10% of a pre-order incentive at both stores; however, owners of the original Alan Wake on PC (from either Steam or GOG) will be able to pre-order American Nightmare for 25% off. Alan Wake is currently available on Steam for 50% off as part of its mid-week madness special.
[Original Story] It would seem Alan Wake isn't finished giving gamers nightmares. A product page has appeared on Steam for Alan Wake's American Nightmare, revealing that the previously XBLA-exclusive adventure is coming to PC.
Remedy confirmed to Joystiq the game will hit PC on May 22.
In April, American Nightmare appeared on the Steam registry, indicating a PC release was imminent. Based on the product description, it doesn't appear that the PC version will feature any new content. American Nightmare is currently available for pre-order on Steam at 10% off its regular $15 price point.