Yesterday we had a first taste with the introduction of Mechromancer but soon we will be able to get my hands on a more full-bodied DLC for Borderlands 2 . Through the publication of new achievements suggests that the upcoming DLC will be "Captain Scarlett and Her Pirate's Booty" which will introduce a new area called Oasis. By the way some users of forum Gearbox found in the PC version of the game files that introduces this new expansion:

"The legends speak of the lost treasure of Captain Blade, a prize so great that men tingerebbero red sand just to have it. A Pirate Queen, courageous and deadly that they would stop at nothing to get it. A Leviathan. Crypt hunters hunters who traveled to the town of Oasis in the wilderness without knowing the horrors that would cut down on them ".

It also seems that the expansion will introduce a new head for each class, a new level of rarity, new items and weapons. We will know more when Gearbox will make the official announcement and maybe we will reveal the release date.