On May 1, 2012, Bethesda announced that the first DLC content for Skyrim, Dawnguard, will launch first for Xbox 360 on the 26th June 2012 and will remain exclusive to that platform for 30 days until its release on PS3 and PC.
Players will be given the choice of joining forces with the Vampires, or alternatively, an order of Vampire hunters known as the Dawnguard. Depending on the player character's choice, they will be granted access to two home bases, Castle Volkihar and Fort Dawnguard, respectively. New armors, perks and weapons, including a crossbow for the Dawnguard, will also be introduced. Additionally, in the case of the Vampires, a transformation into a "Vampire Lord" demon will be made available, working in a similar way to the existing Werewolf transformation. The Vampire Lord will have a new skill tree to level up, as well as a separate skill tree being implemented for Werewolves, with both levelling up individually from the regular skill trees.
Dawnguard will be available on Xbox LIVE for 1,600 MS Points or PSN/PC download for $20.
You can watch the Official Trailer Here