Irrational Games released the first 5 minutes of BioShock Infinite's two-part story DLC. It's called Burial at Sea, and you revisit a very memorable place. WARNING: A bit of spoilers if you haven't touched the original game.
I'm pretty excited about this. Mainly because we get to experience Rapture in its prime, before everything went to hell. You control Booker Dewitt yet again, but this time you get hired by Elizabeth to find a girl named Sally. Interesting stuff, hopefully Irrational Games won't take a long time in developing it.
Burial at Sea is broken into two episodes; you playing as Booker Dewitt for the first episode, then for the first time control Elizabeth for the last episode. No release date was given so far, but it's planned to hit this year.