Planks strengthen your core and sculpt your midsection. It works your rectus abdominis, transverse abdominis, and obliques.
The Russian twist is a wonderful rotating dynamic core workout for obliques and V-taper definition.
The hanging leg raise is a tough but effective lower abdomen and hip flexor workout. For maximum results, I always include these muscles in core activities.
Side planks are an excellent exercise for targeting the oblique muscles as well as your quadratus lumborum, a deep core stabilizer in your lower back.
Bicycle crunches combine a traditional ab crunch with leg and rotational components. They target your entire core region for some serious midsection sculpting.