You can add variety to your ab routine any number of ways: alternating heavy-weight and body weight (higher-rep) workouts, training just one area on a given day (say upper abs on Monday, lower abs on Wednesday), or even working from the most difficult movements to easier ones in a given workout.
Don't forget that while you can emphasize certain areas of your abs, you can't isolate them, so even the lower abs get worked (though to a lesser degree) in most upper-ab movements.
And as for chiseling your waistline, you'll have to get on the treadmill, do some HIIT, and tighten up your diet like the rest of us.
Here are some more tips on how to target your abs: 1) To hit the upper abs, you need to stabilize your lower body.
Crunch your hips toward your pelvis, actually rounding your lower back as you crunch down.
The best exercises to hit the upper abs include: Cable crunches, floor and decline-bench crunches (holding a weight plate) and machine crunches.
2) Conversely, in order to hit the lower abs you need to stabilize your upper body and bring your knees into your chest.
The best exercises to target the lower abs include: hanging knee and leg raises, reverse crunches (use an incline board for more difficulty) and knee ups with a dumbbell between your feet.
3) To hit the obliques, you need to include twisting movements in your workout.
Twisting movements is the best way to emphasize the obliques.
The best exercises for obliques include: Side bends and oblique crunches in which you work in the lateral plane and rotating your torso (as in the cable wood chop).
The obliques commonly receive work when added to a lower - or upper-ab exercise, such as decline twisting crunches.