Box Jumps: Box Jumps - ATHLETE365.com - YouTube
Single Leg Squat, Rear Leg Elevated: 1 leg squat - rear leg elevated - YouTube
Bosu Squats: BOSU Balance Trainer Squats Round - YouTube
Swiss Ball Curls: Swiss Ball Hamstring Curls - YouTube
Single Stiff Leg Deadlift: Single leg deadlift - YouTube
Once you get your balance you can add weight to some of these by holding dumbells and/or doing them more slowly. Doing stuff like this is a great way to change up a typical heavy leg training routine.