Which credit card is accepted more often in Prague? Visa, Mastercard, American Express? Is there a special card that is used there? Are traveler's checks used there?
I don't carry an American Express card, so I can't comment on that one. Both Visa and Mastercard are accepted in Prague and I think that Mastercard is probably accepted more often. You could bring traveler's checks (American Express) as backup, but I suggest using an ATM card, such as one on the Plus system (Visa) or Cirrus/Maestro (Mastercard) to get your money. You would not have to carry around lots of cash as ATMs are all over the place. Just make sure you know the ATM card fees.
I agree on Mastercard for a credit card. ATM machines can be found everywhere, even in lots of small villages. If your card has the Cirrus/Maestro (Mastercard) logo on it, you'll be fine