I rather like this feature from CitiBank. I hate the interface, but the feature is great. I can use it to sign up for monthly services that I'm unsure about. If I don't want to go through the hassle of canceling the service, I just don't renew the cards.

I also use it with sites I don't necessarily trust, like a random auto parts store. If it were a tad easier to use, I'd use it for nearly everything.