Since most people want good abdominal tone more than freaky abdominal size, it probably makes sense to exercise the abs with lower intensity and more frequently, rather than with high intensity and less frequently. You can't just remove the fat from that area on its own. Legendary Abs claims that side bends develop the oblique muscles under the fat and therefore make the fat more prominent, but some people feel that the obliques simply can't get big enough to be noticeable. If anyone feels they can offer an authoritative answer on this question, please contribute. Thanks for asking.
Hyperextensions are a good lower back exercise.
Deadlifts, both straight and bent-legged give the lower back a lot of exercise, so if you do them you don't need to add anything else. Make sure you get someone to show you how to do them properly and keep your lower back arched through the whole movement. For more details consult the misc.fitness FAQ which contains extensive descriptions of both sorts of deadlifts and lots more besides. Lie face down, with your hands touching the sides of your head and your body draped over the edge of the bench. Make sure your hips are supported so your pelvis can't move.