There are two companies offering discount cards for visitors to Prague. You can buy a special tourist card for visitors called a Matilda card (Prague Card) which provides entry to most major attractions for significantly reduced rates plus free city transport for a fixed price of 790 CZK for adults and 530 CZK for children and students. This card is valid for 3 days. Similarly there is the Passport Card. You can buy both of these at PIS tourist information offices and other tourists spots or at AMEX branches. If you are planning to see some tourist attractions and will be using public transport then these are good value for money.

Card issuer: Prague Card
Card name: Prague Card (TM) (also known as Matilda Card)
Validity: 4 Days
Cost: 790Kc (530kc for students).
Discounts: Pass provides free entry to Prague Castle, heavily discounted or free entry to all the city's major museums and historic buildings. Public travel pass is not included but can be ordered in you pay extra depending on the duration you want.
Recommended:  YES

Card issuer: Reklama
Card name: Prague Card & Prague Passport
Validity: 1 year (includes 2x 24 hour travel passes)
Cost: 860Kc
Discounts: Similar discounts as previous card but in less quantity but still good value. Come with a limited medical insurance. Also includes discounts for walking tours, bars, restaurants, hotels and clubs.
Recommended:  NOT NECESSARILY