Side kicks, performed properly are a workout in their own right. You can perform them slowly for a muscle control and balance workout or go flat out for a totally aerobic experience. 

What's involved: Quads, glutes, side hip flexors, lower back, obliques, hamstrings, calves. 

Powered by: Side hip flexors, quads.

Tip: Shape your foot as you are kicking out so that your imagined impact point is the blade of the foot, rather than the flat of the foot. Retract the leg as fast as you send it out.