I wouldn't give a site my credit card just to comment, but I'd be ok with SMS verification. eg. Provide your mobile number when you sign up and they text you an unlock code before it works. Alternatively you could text them first to get the unlock code. The advantage of using SMS verification is it continues to allow anonymous comments, but it's non-trivial to create multiple accounts and losing karma/being banned would be effectively permanent.
You can't automatically retrieve someone's name with their cellphone/mobile number in the way you can with a credit card check, but admittedly it's not very hard. Removing the risk of being ripped off is the major benefit over a cc check.
