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.