It is possible to get a flat stomach and toned abs without the use of any exercise machines.
Most exercise machines promise you amazing results in an unrealistically short amount of time, and write a little text at the bottom that says something like "Your individual results may vary".
Whatever the reason may be, such promises only contribute to the myth that all you need is a piece of abdominal training equipment to get great abs.
The truth is that most exercise machines (there are a few exceptions) aren't any better then regular ab exercises using your body weight alone. Some abdominal machines are much less effective than regular crunches.
This may come as a surprise to you but the best piece of abdominal equipment is a large exercise ball. Not the AB-CRUCH4000 or whatever they try to sell you right now on TV.
Getting great abs is not as easy as they try to make it, ask any fitness model from those same infomercials. Another thing they neglect to mention is that it takes a healthy diet and full body exercise to burn the fat in the first place.
But I am not trying to discourage you, I am trying to help you look beyond the bs and realize that all you need is to be determined, to work hard and you will get great results. If you are determined to get a flat stomach you don't need any special equipment, and if you aren't then no exercise machine will help anyway.
The basic abdominal workout, that can be found on this site or elsewhere is enough for most people.
When you start to get strong abs, you may want to use a piece of ab equipment to give you a higher challenge, but even then you need to choose carefully.
Abdominal Exercise Equipment - How do I determine what works?
To evaluate whether a machine is worth using should be reasonably simple. If it encourages an ab contraction under a load it is good, if not don't bother. An ab contraction is when the sternum is pulled toward the pubic bone or vice versa as the main action.
The exercise Ball
Like I said before, this is the best piece of equipment for your abs.
You can do various abdominal exercises with an exercise ball. Choose an exercise ball that allows your knees to be at a right angle when you sit on the ball with your feet on the floor. The firmer the fitness ball, the more difficult the exercise will be.
Sample Exercise ball exercise: Sit on the exercise ball with your feet resting on the floor, about hip-width apart. Keep your back straight. Cross your arms on your chest. Tighten your abdominal muscles, and lean back until your abdominal muscles kick in. Hold for three deep breaths. Return to the start position and repeat 10-15 times. As you get stronger, gradually increase the number of repetitions and sets. Remember to breathe freely and deeply during the exercise.