Slider, Beijing is full of museums, some quite big and boring, others small and tucked away in hidden out of the way places.  If you want to be overwhelmed or underwhelmed, try any of the larger museums in the city.

But my own personal favorites are as follows -- both are small, intimate and they give me a distance feeling for two important periods in Chinese history:

(a)  the museum in the residence of the late Soong Chin Lin, the wife of Sun Yat-Sen; and

(b) the Imperial City Museum, a small museum that hosts a nice but interesting collection of various vestimentary objects from the Imperial Period.

you can also try the Military Museum

Mao Museum and the other museum the architectural and artifact museum at tiananmen square.