Another exercise that works great are "stair steppers." If you go to a gym that has a platform for these, use it. Otherwise, try to find something that's similar in height in your home and use that. My regular workout includes these, with 4 sets of 10 reps on each leg. When you start doing them, it can be quite hard depending on your flexibility and overall strength, since you're literally putting your entire body weight on one leg. But along with squat jumps, they really do work.