Ellen Mclain, the voice of GLaDOS in the Portal series is back at valve for some work on a new game aswell as some Portal voiceovers as in this tweet by her husband.
“Ellen is going in Tuesday for a new game and more Portal work”.
Though this doesn't really cover much as she is a highly favorited voice actor of Valve meaning that the new game could be anything Valve throws at us. Knowing that Ellen is down doing some Portal work though brings us to the conclusion that it will be some Portal 2 DLC in the near future after the appalling first DLC pack for Portal 2 which was only compatible with the $140 Razer Hydra PC controller.
We can only hope its part of the great free DLC that valve announced back in May.