According to a report by JustPushStart, Batman: Arkham Asylum will be receiving brand new DLC soon, and that it'll be available for the nice sum of free.
What shape or form the DLC will take is unknown.
Go through the link for more info.
The game's out next week for PS3 and 360. The PC version was delayed until September.
If you want to find out more info on the game, listen to the podcast from two weeks ago. It feautres an interview with Batman: Arkahm Asylum PR rep, Gareth Williams.