Ellen McLain is well known in the gaming community as the voice actor behind GLaDOS along with the overseer in Half-Life and the Announcer in Team Fortress 2. And it seems like Mrs. McLain is working on something Portal related again.
John Lowrie, McLain's husband, tweeted this, "Ellen is going in Tuesday for a new game and more Portal work".
Tons of speculation will arise from just this little sentence. She's working on a new game and doign more Portal stuff. All the speculation could be from Half-Life 3, Portal 2 DLC and something not Valve related at all. It might even be another soundtrack for Portal 2.
Fun Fact for you readers. John Lawrie is the voice of Sniper in Team Fortress 2. :D