STYLETHREAD -- LET'S TALK SHOP!

For lower back, I like doing the reverse crunches -- the sit-ups for your back. There's that contraption at the gym that you hook your feet under and lie belly down on the hip pads and slowly raise and lower your upper body using the muscles in your lower back. You can hold extra weights to your chest while you do this, too.

Do you have a balance ball?  If not itis cheap and a great thing to have at home.  You can do a reverse crunch on the ball.  Lay face down on the ball and roll back so your feet (balls of feet and toes) are secure on the ground (if you are wearing shoes you get better traction).  You can place your hands on your lower back or behing your head.  Lift your upper body, your hips/lower abdomen are your support on the ball.  I hope this makes sense.  You'll probably get a better feel for it once you are on the ball. 

Also, kickboxing and yoga are great for all over toning.  Make sure you work some sort of cardio in.

The superman is a good suggestion and to add on to that move.....when you are in the position shown in the picture to go the next step, bend your knees (bringing your heels toward your butt) and pull your elbows back.  This really engages your whole back.  You will feel it.