Well the 1st dlc called "Bug Hunt" is suppost to be out this tuesday (19th), people who pre-ordered the game from walmart got a code to download bug hunt early which was usable on friday, so far reviews of it have been mixed and not as fun as other games horde modes, Ai has apparently improved though. There are videos of it on youtube.
No idea about future dlc... or even if there will be any now, after how bad the game has become. They arent even giving out shift codes, but they seem to put Borderland 2 ones on everyday, Now with a new game out you would expect more than 1 shift code to be released!?! I do enjoy this game as I am an aliens fan but I can really see this game being forgotten about.