Dead Space 2 releases today, and the first DLC pack for the game has already been announced. Titled "Severed", the add-on will feature two new single player chapters that star the main characters of the Wii game Dead Space: Extraction; Gabe Weller and Lexine Murdock. Their chapter will run alongside Isaac's in the full game, so you'll be able to see more insight to what's going on. No date or pricing details have been announced at this time.
I'm going to leave the launch day DLC announcement with a personal "No Comment", I have to admit it's pretty cool to see them tying the franchise together more tightly like this.