Does anyone know if ANY of those ab machines that you see on the infomercials actually WORK? Or are they a complete waste of money?

Work for what specifically?

Spot reduction of a fat stomach---No.

Building up the abs---Yes.

It really depends on what you're looking for. Both as was said above and in the type of workout/help you want.

If you're looking for something to add resistance to your ab excercises, as most of them claim to do, then most of them are a waste of your money. If you are just looking for something to help you keep proper form, then most of them will do the job. Of course, I have not tried all of them, or even most of them, so there may be some exceptions.

My rule of thumb...if a piece of exercise equipment can be had for a few "easy payments of $19.99", then it is not worth having.

There is no truth in advertising, so use a little basic common sense when evaluating a product. Do they have testimonials of people losing huge amounts of weight/inches from using the product? Do they promise amazing results in a short period of time? You know the drill. If it sounds too good to be true, then it probably is.