I've thought the same thing. Why isn't there a system that requires a small inconvenience or effort before a particular transaction goes through? Example: I go to buy something online, but before the money really goes from me to the merchant, I have to phone in, identify/authenticate myself, and identify some transaction details (perhaps an ID, the dollar amount, the merchant's name).

I'd be happy to go through a few minutes of inconvenience for a large purchase if it meant significantly greater security for my credit card.