-100 crunches on a swiss ball
Lay on a swiss ball so that your butt is just barely on the ball. to avoid stress on the neck, keep your back straight and pull your torso forward using your abs. I like this method instead of bringing the shoulders forward because it promotes good posture.
-75 flutter kicks
Lay flat on your back. You may place your hands under your hips to assist yourself. Keeping each leg straight (do not bend at the knees), alternate raising each leg to 90 degrees. This not only will not build a strong core, but will also help with flexibility.
-100 oblique crunches (50 each side)
This move is slightly different from the regular swiss ball crunch. Here, you want to crunch at your sides pulling in with both your torso and your legs (crunch at about a 45 degree angle to target the obliques).
-25 suitcase crunches (if you're a beginner, try doing two sets of 12 with this)
Lay flat on your back. Simultaneously bring your knees to your chest and perform a normal crunch then release both of these as you extend your legs straight out (6 inches off the ground) and your arms straight out behind your head.)
-50 crunches on the swiss ball with a 25 lb plate
Use the same form as the crunches mentioned above. Add more resistance by holding a 25 lb plate high on your chest (comfortably under the chin) with your arms crossed over it.
-50 flutter kicks
-25 crossovers with 25 lb plate
Sit on the ground holding a 25 lb plate, and while keeping the legs elevated, touch the plate beside each hip.
To add an extra challenge perform 2 sets of side planks (left and right) and front planks, 30 seconds each.
This is a great way to finish an ab routine. Not only are you working your abs, but you are stabilizing your shoulders. These are great for burning fat and creating better definition in the midsection. Here is a link that will show you a proper plank. http://www.abs-exercise-advice.com/plank.html
Remember: The goal is 500 quality reps. Again, there are many options as far as what exercises you can do--just as long as a minimum 500 reps are completed. Focus on form and good posture. If you're feeling great, go for 700.
I will add more advanced 500 rep workouts soon. These will suggest going above 500 repetitions and also will feature more challenging exercises.