A fresh update for the PC version of Portal 2 adds two-controller split-screen co-op to the acclaimed puzzler, as well as support for the recently launched Big Picture mode. So, now you and your buddy or ladyfriend or RealDoll can play in the same room from the comfort of your couch.
To activate this newfound method of co-op play, enter the co-op menu, then press X on the second controller. After that, you should both be good to go.
The update also fixes a couple bugs related to the controller and movement stopping and exiting and entering certain menus. Boot Steam to grab it now.