we will have a 4 day trip to beijing on march 2013,what is the best itinerary you can recommend to

Hi, you can surely go to Shanghai for a one-day trip. Never miss the Bund, the Oriental Pearl Tower there.
For the itinerary in Peking, here is my suggestion:
D1, Badaling Great Wall and Temple of Heaven
D2, Tiananmen Square and the Forbidden City. And then the Summer Palace
D3, Beihai Park and Shichahai as well as the Hutongs and Courtyards
You can refer to the website below to know more:
https://www.travelchinaguide.com/package/beijing.htm