Got this from iVillage:
How can I tone my butt? What exercises can I do in the gym and at home that will make it more perky?
Squats are my favorite lower body exercise. They recruit more of your large leg muscles than any other exercise and are great butt toners. You can do squats in the gym or at home. You can do them with your own body weight, while holding dumbbells in your hands, or, for more resistance, with a barbell across the back of your shoulders (use a spotter when you do this).
Here's how to do a squat:
1. Stand with your legs shoulder width apart (wider if you have long legs) and your feet parallel, or slightly turned out.
2. Cross your arms in front of your chest, or hold dumbbells in your hands and rest them on your hips.
3. Inhale as you squat, going no lower than the point at which your thighs are parallel to the floor. Keep your head up and your back straight. One way to keep your head up is to focus on a point high on the wall, near where it meets the ceiling (unless you're training in the Astrodome).
4. Exhale as you stand up. Straighten your legs completely, but don't lock your knees. Also, make sure your knees don't jut out beyond your toes. This avoids knee strain (which is also the main reason for not going lower than knees parallel to the ground) and won't recruit your hip extensors as much. Do up to 3 sets of 12-15 repetitions.
Squats are a power exercise, and you should eventually do them with some added resistance. There is a lot to keep track of while doing squats. It is very helpful to do them in front of a mirror.
One tried and true floor exercise that works your butt is the kickback. Start out on a mat on your hands and knees, with your weight evenly distributed among your points of support. Draw one knee forward underneath you as far as you can, and then extend your leg straight behind you. Although the exercise is called a kickback, the extension of your leg should be smooth and gentle. Avoid excessively arching or rounding your back while doing this routine. Do this on one side for 15-25 repetitions, and then change to the other side. When this gets easy, wear ankle weights for more resistance.
For more exercises to do at home, check out videos pertaining to this area from The Firm series and Kathy Smith.
Finally, if you want to have fun and work your butt at the same time, try in-line skating. If you skate with good form (back flat, legs tucked under the body before the stride is initiated), you'll get a tremendous glute workout, as well as important aerobic exercise.
