I love working out, especially my abs. I'm always trying to achieve a 6 pack. Its important to maintain a strong core to eliminate any back pains, helps you perform better in sports, helps avoid injuries, and can also improve your balance.
For my general ab work out I have a few different routines. Its important to mix it up so that your body doesn't plateau. This is #1 of my routine for my abs. I tend to warm up for 5-10 minutes (either with running, jumping jacks, or dancing). I then proceed with 3 (1 minute interval) planks. If your not use to doing the plank, then try 30 seconds and try to do as many intervals as possible. Very important to keep your back straight during the plank. After the 3 minute plank, I stretch, then proceed with standard sit-ups. I tend to do 100 sit ups with 16 lbs. Then I do a reverse crunch (weights on my ankles) and do a 100. Afterwards I tend to do the bicycle crunch for 3 (1 minute intervals). After this I then do a leg lift...this is where I have weights on my ankles and left my legs up, my partner then tries to push my legs down with force, and I have to prevent my legs from hitting the floor and raise them again. I do 75 of these. I then proceed with the vertical leg crunch. I have my legs up in the air and I lift my upper body off the floor to try and hit my feet with my hands. I actually find these more difficult (lol, that could be because I'm tired at this point) so I do only about 50. I then proceed with 50 crunches on the exercise ball. Last but not least I do a 100 dumbbell side bends per side holding onto 12 lbs.
This is an example of one of my routines. I do not use this routine every time I work out my abs because that would not be very effective. Its always best to mix things up and not allow your body to adapt to your work out regimes.