The best lower back exercise, is without a doubt and comes to no surprise. Deadlifts are the best. It is probably the best back exercise in general, and one of the best exercises for the body period.
Though the lower back is targeted, other muscles are worked as well. These include: Calves, forearms, hamstrings, glutes, middle back, lats, traps, and quadriceps. As you can see, deadlifts are one of the key exercises in total body strength, and not just lower back!
The deadlift only requires a barbell and plates. With these two pieces of equipment, you have the ability to to grow your entire body with one exercise.
The deadlift also requires that you keep your back straight at all times. Thus helping you in your every day life. Why you ask? By practicing a stable straight back, your every day activities will benefit because your strict movement with this exercise. Your waist and hips will also strengthen.
Getting back to every day life, this exercise compares to one of the most common motions on a day to day basis. Which is lifting objects off the ground. Your chance of injury can decrease with your day to day activities. Also, unlike the bench press and the squat, you don't suffer the chance of weight being pinned on you. If you need to drop the weight, you can do so without getting hurt.
This exercise will also improve your cardio-respiratory fitness. It can be very intense at times and it will test your cardio-respiratory health for the better.
If you haven't already incorporated the deadlift into your back workout, it is highly recommended you do so. You probably include the bench press in your workouts, your may include the squat as well, so why have you skipped deadlifts?