Tabata
This exercise strategy involves brief bursts of very intense activity, followed by a leisurely stretch of exercise. To get the maximum effect for your legs, use stairs for the intense activity, and then jogging in place (or even using a small trampoline for jumping) for the lighter activity. Most tabata is timed for thirty seconds of intense work and then thirty seconds of something lighter. When you feel comfortable with this you can boost it to a minute each, for a set of three.