I don't know where this is from. But in Portugal, I really feel blessed by the MBNet service that exists here. Basically you tie it to any card (credit/debit) and generate temporary credit card numbers with a hard value limit defined at the time of creation. Want to buy a 10$ game, generate a card with a slightly larger value and pay with it. If the merchant tries to take more, it is denied and the card automatically cancelled.
I am amazed this doesn't exist elsewhere (if it does I have never heard of it). Even banks themselves could provide something like this.
EDIT: I don't know how it actually works if you want to pay by credit. I generally generate cards with values that my bank account can cover.
Bank of America, my credit card provider provides the same sort of service. They call it ShopSafe. You generate a temporary credit card number with a certain limit and you can set when it expires.
It is fantastic for purchasing goods from web sites that may not secure their card data completely, or if you are worried about fraud on the internet. I've also in the past generated the numbers for when I need to pay over the phone and don't want to hand out my credit card number!
Extremely handy, unfortunately it seems that not enough people make use of it, to the point that BoA employees in the fraud department are at times not even aware that the feature exists...
I'd be interested in using this, but I get so frustrated with Bank of America's fees. They want to charge $10/month just for using OFX to access your own financial transactions!
Given the level of security that most banks implement, this is completely indefensible in my books (given that the same information is available through the shoddy web interface).
Whether or not you have a fee for your card itself depends on what card you get; I'm not referring to those kinds of fees.
As for the second point, Mint/Intuit probably covers those fees for their own service, but they don't allow you to interface with them over OFX, so it's a moot point for anyone who wants that information for something other than Mint.
Just to add something regarding MBNet, it is also now possible to create a virtual credit card for multiple transactions, I believe up to a year. But it will never go over whatever limit you set at the beginning. It's a great payment method indeed.
I've used the same feature through Citi credit cards although it's fairly well hidden on their site if I remember correctly. I've never found this feature with my American Express or Chase accounts.
I am amazed this doesn't exist elsewhere (if it does I have never heard of it). Even banks themselves could provide something like this.
EDIT: I don't know how it actually works if you want to pay by credit. I generally generate cards with values that my bank account can cover.