The Lost and Damned will be Xbox LIVE's deal of the week on the week beginning August 24th, so if you're planning to get it then that would be a good time to do so. You will be able to get it for 1200 Microsoft Points ($15.00 USD) as opposed to 1600 Microsoft Points ($20.00 USD) representing a $5.00 price cut.
TLAD is the first episodic expansion of Grand Theft Auto IV, featuring new missions, new weapons, new vehicles, new multiplayer modes and a new main character. It was released in February exclusively for Xbox 360. For more details go here.