Ballet Abs - I don't remember doing any of these separately (except for crunches) when I use to dance. I got my "ballet abs" by holding it in during class for 10 years; however, these exercises are great for anyone.
Tips link: Fastest way to lose 20 pounds, according to Women's Health. Including this body weight workout times a week, doing 2 sets of each exercise with reps per set (Note: 30 sec. plank) to help prevent injuries.