In keeping with the Communist (and Confucian) passion for naming and quantification, Beijing has a museum for everything -- police, bees, even the humble watermelon. If you share this passion and plan on spending a week or more in the capital, invest in a bowuguan tong piao (¥80), which grants you free (or half-price) admission to 98 sites in and around Beijing. You can buy the museum pass at full-service post offices around town.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.