Whenever I ask people what their goals are, I often hear one thing, “I want to lose my stomach”.  Body fat in our abdominal region is called visceral fat and can be dangerous in large amounts.  This type of fat often increases your chances of developing diabetes or any other type of cardiovascular disease.  If we want to lose body fat and strengthen our core muscles, we don’t necessarily have to focus solely on crunches.
Besides cardio equipment, abdominal strength machines are often the most popular pieces of equipment at a gym.  In the fitness world, we often use the term spot reduction to describe clients’ goals.  Spot reduction is the theory that if you want to lose fat in a specific area, then you should perform exercises for that specific area.  This theory is not true.  Specific exercises will help individual muscles, but exercise as a whole and diet are the biggest keys to a smaller waist.  
The best exercises for a strong core are a combination of abdominal machines and crunches, compound exercises, and cardiovascular training.  Ab machines will target your core muscles directly, but compound exercises help not only core muscles but also all of the surrounding muscles that protect your spine.  Examples of compound exercises include squats, deadlifts, shoulder presses, and bench presses. 
Performing cardio will also help burn extra calories, leading to a caloric deficit and ultimately greater weight loss.  If fat loss is your primary concern, steady state training is what you want to focus on.  Steady-state training is performing exercise while keeping your heart rate at +/- 5bpm the entire time, causing fat to be used as fuel.
Diet, as you know, is just as important as anything.  The phrase, “you are what you eat” is true.  If you consume foods that are high in saturated fats and sugars, fat will begin to form around your stomach causing weight gain.  Eating healthy foods, such as fruits and vegetables, will help burn fat faster.  
If you want to lose extra body fat, the keys are lifting weights, performing cardio, and eating a well-balanced diet.  If you are unsure what foods to be eating, always ask your doctor or other medical/fitness professional.  Body fat can be stubborn and may tell you it doesn’t want to go away, but with a little hard work and determination, it can be gone for good!