The source code for Duels of the Planeswalkers 2012 supposedly outs the first DLC pack for the game, according to MTG Salvation forum user "luminum can". It's a triple pack of decks -- standard fare for all you mana tappers out there, including a red/blue, white/green and mono black deck. And if you fear change (hey, we get it -- just thinking about David Bowie gives us the chills), the original decks will each be bolstered by four new cards each.
If you're looking to do some recon, a majority of the cards can be looked up through Gatherer, Wizards of the Coast's search utility for Magic: The Gathering. For the full list of cards found in the files, hit up the source link below.