Getting your lower back into shape is a much overlooked part of anyones training program.  You need these spinal erector muscles to assist you in many other lifts you will perform in your workouts.  Any workout to lose abdominal fat will aid you in strengthening your lower back.  Any exercise you do for your lower back will also build your abdominals.  Exercises like hyper extensions are great to get your lower back strong.  The king of all the back exercises is the best overall lowerback exercise you can do.  The deadlift is the best exercise period if you ask me.