Nwinters - I train my abs 2-4 days a week, and mix it up between weighted ab work, such as situps with a plate behind my head, sidebends, some other different twisting/oblique exercises, and non weighted ground based ab work for high reps... v-ups, atomic situps, jackknifes, leg raises, different static holds (pikes), and a few other movements. I'd like to make my own medicine ball and tornado ball in the future as those are also valuable tools for the abs.