The Scissor Kick is a great exercise to work your lower abs. This exercise can be used in a continuum of ab exercises among other ab exercises and not to be performed as a primary exercise.
The Russian twists are one the most effective core exercises to strengthen your abdominal muscles. This exercise works your upper body and strengthen your core, lower back and hips as well. The only thing you will need for this exercise is a weighted plate.
The Otis-up exercise is a great exercise to work your upper body. This exercise emphasis on the upper abs as the primary muscles worked.
The Lying side oblique crunches focus on the internal and external oblique muscles. In addition, the obliques work at maximum effectiveness when your body does side bending movements. These muscles are located along the sides of the waist.
The landmine 180s are a strength type of exercise that mainly target the abdominals and in addition to the abdominals, you will be exercising your lower back, glutes and shoulders as secondary muscle groups.
The Knee-Hip Raise On Parallel Bars targets the abdominals. In particular, the group of lower abdominal muscles along with the hip flexors will be worked with this exercise.
The jackknife is an advanced abdominal exercise that targets the rectus abdominis, the main abdominal muscle or the six pack. By adding a slight twisting rotation to the standard jackknife, you engage your obliques, or side abs, and target more muscles with one movement. There is no special equipment required to perform this exercise.
The Hanging pike exercises works to strengthen your abs and hip flexors as a unit without requiring you to arch your back.
The hanging leg raise is a core strengthening exercise that targets the entire abdominal region with an emphasis on the lower abs. This exercise also improves stability in the lower back.