I'm not sure if this has been posted yet but free Portal 2 DLC will be available for PC, Xbox Live and PSN on October 4th.
Testing begins anew next week, guys.
And if you've forgotten, this content won't cost you a dime.
If you're playing solo, Valve's included a Challenge Mode with leaderboard functionality. Said Challenge Mode is also available for co-op play, though. Co-op! Co-cop! Co-op!