How to get lean flat abdominals?

I have seen many advertisements about getting flat abdominals. They have fancy machiens and belts that magically create abs. The latest piece of advice that I have gotten is the that you should not do any ab excersises because that would make you get a bigger belly. To me, I have always believed that if you want to get lean abs you should work hard at it. Do ab excercises about twice a week and eat healthy foods, especially vegetables. What is the real truth of getting abdominals? Does anyone have any real life experiences to share about the method they used or are using? That would be really helpful.