Butt Toning Exercise
From iVillage

Question: How do I sculpt my butt?
Answer: Squats

Here's how to do a squat:

Stand with your legs shoulder width apart (wider if you have long legs) and your feet parallel, or slightly turned out.

Cross your arms in front of your chest, or hold dumbbells in your hands and rest them on your hips.

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.

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.