At my gym there is a hack squat machine w/ an incline where you can face 2 ways, forwards and backwards. It looks like something football players use for practice w/ an incline plane 2 stand on. Anyway you face the machine and do step-ups one leg at a time and it really works the ass. I will have 2 find a picture to show u exactly what i mean. Also... lay on the floor on your back and bend your knees. Raise one leg up to about 45-55 degree angle. With the leg that is still on the floor push yourself up, raising your pelvis to the ceiling. Make sure to squeeze that ass though. Do on each side. Along with lounges, squats, and step ups... your ass will become tighter.