Not all banks in the United States support this; but, some allow you to manufacturer a credit card number that is linked to your accout but only worth a definable amount of money.
Bank of America (which I use) allows it at no extra cost for the service. It was developed in response to CC theft over the internet. So, if I use their program to calculate a number and assign it $20 + any extra cost, then that's all its valid for.
