I feel like I should first point out that abs are made in the gym, but uncovered in the kitchen. What you eat is arguably a larger part of the results you will see from your hard work and than the hard work itself. You can do crunches until you are blue in the face, but if you eat garbage, then you'll never see hide nor hair of that already elusive six-pack.
Second, you don't need to do ab work every day. It's actually counter-productive because your muscles need time to repair after a workout so that they can strengthen. That being said, add this workout in a few days a week on non-consecutive days to help shape and strengthen your core.
Planks you can do in a pushup position, or on your elbows lined up directly under your shoulders. Same goes for side planks. If they're too difficult, drop your bottom knee to the ground and keep your top leg straightened out.
Hollow Body Holds~ Lay on your back, lift feet about 6-10 inches off ground while simultaneously lifting head and arms overhead and holding. Don't forget to breath!
Tuck-ups~ Lay flat on your back with legs out straight and arms overhead. Bring knees to chest and sit up to balance on your tailbone before returning to start position to complete one rep.
Bicycles~ Sit up with hands placed on ground behind hips, lean back and start bicycle motion with your elevated feet. A full mock rotation on each leg counts as one. "Pedal" backwards for an additional 20 reps.
Mountain Climbers~ Assume push up position. Alternate pulling knees to chest and tapping foot on ground. the faster you go, the harder they get but be sure to keep your butt flat.
Heels to Ceiling~ These should be felt in the lower abs. Lay flat on your back, raise your legs straight up so that the soles of your feet are parallel with the ceiling. Using your abs, drive your heel straight up to the ceiling (not towards your head).
Seated Twist~ Sit with knees bent, lean back until you feel your core engage, interlace your fingers to make a clasped fist and take your fists right to left tapping the ground gently. Left tap, right tap is one repetition.
You could also add some Superman holds lying flat on your tummy for 30 seconds to this workout as well. This workout is a great compliment to the arm workout and leg workout posted previously.