(ATTN: As confirmed by Sefton Hill of Rocksteady, the Joker will only be playable on the PS3 and will not be playable on the 360 at anytime in the future. It is a permanent PS3-only exclusive. This is due to an exclusive deal that Sony has for the video game.)
There will be Physx implementation for users with nVidia 8800+ graphic cards, or Ageia Physx Cards (if anyone ever bought these before nVidia bought the company).
Able to play as The Joker in eight Challenge Map which will be released as downloadable content on August 25th on the PlayStation Network. This DLC will be free.
There will be a "Batman Arkham Asylum Batcave Outpost Apartment". Apparently, this will be only for PlayStation Home. It will contain items such as the Batsuit, Batmobile, and Batwing, along with various Bat-gadgets. This content on PlayStation Home will be free.
The comic book "The Road to Arkham" will be given to PSP owners via download on the PlayStation Network. This comic will be free but will most likely NOT be able to be read by your PS3.
The PlayStation 3 version of Batman: Arkham Asylum will use some elements of SIXAXIS Motion Control.
Found this news here