Rockstar Games have dated Grand Theft Auto IV: The Ballad of Gay Tony for October 29th, exclusive to the Xbox 360.
As well as the DLC expansion, they also dated their standalone game, Episodes from Liberty City, for October 29th. The game sees both The Ballad of Gay Tony and earlier expansion, The Lost and Damned, coming to the Xbox 360 in a single disc, which doesnt need Grand Theft Auto IV.
That is also exclusive to the 360.
Both expansion and Episodes from Liberty City were announced back in May.