The I amsterdam City Card provides free and discount admissions to many of Amsterdam's top museums (but not the Anne Frank House), plus a free canal ride, free use of public transport, and a 25% discount on various attractions and restaurants; savings can be very substantial. A 24-hour pass costs €40, a 48-hour costs €50, and a 72-hour costs €60. The pass comes with a booklet in Dutch, English, French, German, Italian, and Spanish. It can be purchased at branches of the VVV (Netherlands Board of Tourism information offices), the GVB (both at Centraal Station), and through some hotels and museums.
If you are here for a few more days or intend to visit museums in other parts of the Netherlands, such as Haarlem, a Museumkaart (museum card) might offer better value. This gives you free entry to more than 440 museums throughout the country for a year, including the top draws in Amsterdam (except the Anne Frank House). It is available, upon showing ID, at VVV offices and participating museums for €44.95.