Get in a pool!!! My husband had his repaired on 6/7/11 and he is within 30 degrees of having the same flex/retract on both knees. The pool has been great for him. He goes to PT once a week and the pool has done 10x as much for him as PT does.
Just get in and walk. He goes for 30-45 minutes and there is no impact on the knee at all. He just walks up and down one side of the pool in the shallow end.