If you are visiting from a foreign country then the current exchange rate will be of interest to you. Here is a guide to some of those services including our very own pocket sized printable currency cheat sheet for conversion between the Czech Koruna and the US Dollar / UK Pound / Euro Prague has several major foreign money exchange banks:
American Express, Thomas Cook, Ceska Obchodni Banka, Komercni Banka and Zivnostenska Banka
Banks can charge in the region of 2-4% commission for foreign cash exchanges.
Beware of unscrupulous exchange bureaux, the big 0% commission sign you see usually applies only to changing Czech crowns to foreign currency, not the more common direction of changing foreign currency to crowns. They are perfectly able to advertise in this way, and if you're not careful you could find yourself paying up to 9% in commission. We recommend Camfex Group on Vladislavova, who charge 0% commission on buy and sell, and have the best retail rates in Prague.
For specific information on the the Czech currency click here