Signing up for on-line services is a good use for "virtual account numbers". This is a feature offered on some Citibank and Discover credit cards (maybe others) that allows you to generate a separate credit card number that's billed to your original account. The nice thing about them is that once a virtual account number has been billed by a vendor, it does not accept any charges in the future except from the same ve…
Downside, none of their service reps even know it exists, even worse they are slowly phasing it out (making it more and more difficult to find) even-though it is a feature I absolutely love.