The reverse leg kick is perfect for working the glutes/butt. It is very easy to perform, and is one of the few exercises that works the glute muscles exclusively [with assistance from the hamstring muscles].
Begin by placing one knee on a weight bench. Use your hands to support your upper body. The toe of the "working leg" should lightly touch the floor. In one sweeping motion, keep the leg straight and slowly kick backwards until it is even with the back.
As you kick the leg back, try to manually contract or squeeze the glute muscle, as it will enhance the exercise. Slowly lower the leg, tap the toe on the floor, and repeat the exercise. Be sure to control the speed of the leg at all times. Never rush this exercise. You should breathe out as you kick your leg back.
Place one knee on bench. Support upper body with hands. Toe of "working leg" should tap floor.
Slowly kick the leg backward until it is straight. Exhale.
Lower the leg, tap the toe, and repeat several times.