Try CitiVAN (Score 4, Informative)

Citibank offers a "Virtual Account Number" service for their credit cards (Mastercard). It works fairly well. You can do one-shot purchases, or recurring purchases with the same merchant only, or even cap the total you're willing to spend via a virtual number over a number of months.

They have a web interface, but you can also download a Java applet that can generate numbers and fill in purchase forms for you.